CI wheel builder failure on Linux Python 3.11 3.12 and 3.13 with `BrokenProcessPool`

last successful on October 22 [build log](https://github.com/scikit-learn/scikit-learn/actions/runs/18704782622/job/53340764569)

first failing on October 23 [build log](https://github.com/scikit-learn/scikit-learn/actions/runs/18736923722/job/53445538260)

Unclear what the root cause is for now (identical versions it seems, the Python 3.11 build has a different Python bugfix version but I think this is a red herring since Python 3.12 and Python 3.13 have the same bugfix version) ...

Failing tests:
```

  FAILED inspection/tests/test_permutation_importance.py::test_permutation_importance_equivalence_array_dataframe[0.5-2]
  FAILED inspection/tests/test_permutation_importance.py::test_permutation_importance_equivalence_array_dataframe[1.0-2]
```

```
________ test_permutation_importance_equivalence_array_dataframe[0.5-2] ________
  joblib.externals.loky.process_executor._RemoteTraceback: 
  """
  Traceback (most recent call last):
    File "/tmp/tmp.q3sHOyewIE/venv/lib/python3.13/site-packages/joblib/externals/loky/process_executor.py", line 453, in _process_worker
      call_item = call_queue.get(block=True, timeout=timeout)
    File "/opt/_internal/cpython-3.13.8/lib/python3.13/multiprocessing/queues.py", line 120, in get
      return _ForkingPickler.loads(res)
             ~~~~~~~~~~~~~~~~~~~~~^^^^^
    File "/tmp/tmp.q3sHOyewIE/venv/lib/python3.13/site-packages/pandas/core/arrays/categorical.py", line 1726, in __setstate__
      return super().__setstate__(state)
             ~~~~~~~~~~~~~~~~~~~~^^^^^^^
    File "pandas/_libs/arrays.pyx", line 85, in pandas._libs.arrays.NDArrayBacked.__setstate__
    File "pandas/_libs/arrays.pyx", line 103, in pandas._libs.arrays.NDArrayBacked.__setstate__
  NotImplementedError: (CategoricalDtype(categories=[0.0, 1.0, 2.0], ordered=False, categories_dtype=float64), array([1, 0, 2, 1, 0, 2, 2, 1, 0, 1, 2, 1, 2, 0, 0, 1, 1, 0, 1, 2, 2, 0,
         1, 2, 2, 0, 2, 1, 2, 0, 0, 2, 2, 2, 2, 2, 1, 1, 1, 1, 0, 1, 1, 0,
         1, 0, 1, 1, 1, 2, 1, 0, 1, 0, 2, 0, 1, 1, 2, 1, 1, 1, 0, 0, 0, 2,
         0, 0, 2, 2, 0, 0, 0, 0, 2, 2, 0, 0, 2, 2, 1, 0, 0, 0, 1, 2, 0, 2,
         1, 0, 0, 1, 1, 2, 2, 2, 1, 2, 2, 2], dtype=int8))
  """
  
  The above exception was the direct cause of the following exception:
  
  n_jobs = 2, max_samples = 0.5
  
      @pytest.mark.parametrize("n_jobs", [None, 1, 2])
      @pytest.mark.parametrize("max_samples", [0.5, 1.0])
      def test_permutation_importance_equivalence_array_dataframe(n_jobs, max_samples):
          # This test checks that the column shuffling logic has the same behavior
          # both a dataframe and a simple numpy array.
          pd = pytest.importorskip("pandas")
      
          # regression test to make sure that sequential and parallel calls will
          # output the same results.
          X, y = make_regression(n_samples=100, n_features=5, random_state=0)
          X_df = pd.DataFrame(X)
      
          # Add a categorical feature that is statistically linked to y:
          binner = KBinsDiscretizer(
              n_bins=3,
              encode="ordinal",
              quantile_method="averaged_inverted_cdf",
          )
          cat_column = binner.fit_transform(y.reshape(-1, 1))
      
          # Concatenate the extra column to the numpy array: integers will be
          # cast to float values
          X = np.hstack([X, cat_column])
          assert X.dtype.kind == "f"
      
          # Insert extra column as a non-numpy-native dtype:
          cat_column = pd.Categorical(cat_column.ravel())
          new_col_idx = len(X_df.columns)
          X_df[new_col_idx] = cat_column
          assert X_df[new_col_idx].dtype == cat_column.dtype
      
          # Stich an arbitrary index to the dataframe:
          X_df.index = np.arange(len(X_df)).astype(str)
      
          rf = RandomForestRegressor(n_estimators=5, max_depth=3, random_state=0)
          rf.fit(X, y)
      
          n_repeats = 3
          importance_array = permutation_importance(
              rf,
              X,
              y,
              n_repeats=n_repeats,
              random_state=0,
              n_jobs=n_jobs,
              max_samples=max_samples,
          )
      
          # First check that the problem is structured enough and that the model is
          # complex enough to not yield trivial, constant importances:
          imp_min = importance_array["importances"].min()
          imp_max = importance_array["importances"].max()
          assert imp_max - imp_min > 0.3
      
          # Now check that importances computed on dataframe matche the values
          # of those computed on the array with the same data.
  >       importance_dataframe = permutation_importance(
              rf,
              X_df,
              y,
              n_repeats=n_repeats,
              random_state=0,
              n_jobs=n_jobs,
              max_samples=max_samples,
          )
  
  ../venv/lib/python3.13/site-packages/sklearn/inspection/tests/test_permutation_importance.py:357: 
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
  ../venv/lib/python3.13/site-packages/sklearn/utils/_param_validation.py:218: in wrapper
      return func(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^
  ../venv/lib/python3.13/site-packages/sklearn/inspection/_permutation_importance.py:288: in permutation_importance
      scores = Parallel(n_jobs=n_jobs)(
  ../venv/lib/python3.13/site-packages/sklearn/utils/parallel.py:91: in __call__
      return super().__call__(iterable_with_config_and_warning_filters)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:2072: in __call__
      return output if self.return_generator else list(output)
                                                  ^^^^^^^^^^^^
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:1682: in _get_outputs
      yield from self._retrieve()
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:1784: in _retrieve
      self._raise_error_fast()
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:1859: in _raise_error_fast
      error_job.get_result(self.timeout)
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:758: in get_result
      return self._return_or_raise()
             ^^^^^^^^^^^^^^^^^^^^^^^
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
  
  self = <joblib.parallel.BatchCompletionCallBack object at 0x7f8c44e4d6d0>
  
      def _return_or_raise(self):
          try:
              if self.status == TASK_ERROR:
  >               raise self._result
  E               joblib.externals.loky.process_executor.BrokenProcessPool: A task has failed to un-serialize. Please ensure that the arguments of the function are all picklable.
  
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:773: BrokenProcessPool
  ________ test_permutation_importance_equivalence_array_dataframe[1.0-2] ________
  joblib.externals.loky.process_executor._RemoteTraceback: 
  """
  Traceback (most recent call last):
    File "/tmp/tmp.q3sHOyewIE/venv/lib/python3.13/site-packages/joblib/externals/loky/process_executor.py", line 453, in _process_worker
      call_item = call_queue.get(block=True, timeout=timeout)
    File "/opt/_internal/cpython-3.13.8/lib/python3.13/multiprocessing/queues.py", line 120, in get
      return _ForkingPickler.loads(res)
             ~~~~~~~~~~~~~~~~~~~~~^^^^^
    File "/tmp/tmp.q3sHOyewIE/venv/lib/python3.13/site-packages/pandas/core/arrays/categorical.py", line 1726, in __setstate__
      return super().__setstate__(state)
             ~~~~~~~~~~~~~~~~~~~~^^^^^^^
    File "pandas/_libs/arrays.pyx", line 85, in pandas._libs.arrays.NDArrayBacked.__setstate__
    File "pandas/_libs/arrays.pyx", line 103, in pandas._libs.arrays.NDArrayBacked.__setstate__
  NotImplementedError: (CategoricalDtype(categories=[0.0, 1.0, 2.0], ordered=False, categories_dtype=float64), array([1, 0, 2, 1, 0, 2, 2, 1, 0, 1, 2, 1, 2, 0, 0, 1, 1, 0, 1, 2, 2, 0,
         1, 2, 2, 0, 2, 1, 2, 0, 0, 2, 2, 2, 2, 2, 1, 1, 1, 1, 0, 1, 1, 0,
         1, 0, 1, 1, 1, 2, 1, 0, 1, 0, 2, 0, 1, 1, 2, 1, 1, 1, 0, 0, 0, 2,
         0, 0, 2, 2, 0, 0, 0, 0, 2, 2, 0, 0, 2, 2, 1, 0, 0, 0, 1, 2, 0, 2,
         1, 0, 0, 1, 1, 2, 2, 2, 1, 2, 2, 2], dtype=int8))
  """
  
  The above exception was the direct cause of the following exception:
  
  n_jobs = 2, max_samples = 1.0
  
      @pytest.mark.parametrize("n_jobs", [None, 1, 2])
      @pytest.mark.parametrize("max_samples", [0.5, 1.0])
      def test_permutation_importance_equivalence_array_dataframe(n_jobs, max_samples):
          # This test checks that the column shuffling logic has the same behavior
          # both a dataframe and a simple numpy array.
          pd = pytest.importorskip("pandas")
      
          # regression test to make sure that sequential and parallel calls will
          # output the same results.
          X, y = make_regression(n_samples=100, n_features=5, random_state=0)
          X_df = pd.DataFrame(X)
      
          # Add a categorical feature that is statistically linked to y:
          binner = KBinsDiscretizer(
              n_bins=3,
              encode="ordinal",
              quantile_method="averaged_inverted_cdf",
          )
          cat_column = binner.fit_transform(y.reshape(-1, 1))
      
          # Concatenate the extra column to the numpy array: integers will be
          # cast to float values
          X = np.hstack([X, cat_column])
          assert X.dtype.kind == "f"
      
          # Insert extra column as a non-numpy-native dtype:
          cat_column = pd.Categorical(cat_column.ravel())
          new_col_idx = len(X_df.columns)
          X_df[new_col_idx] = cat_column
          assert X_df[new_col_idx].dtype == cat_column.dtype
      
          # Stich an arbitrary index to the dataframe:
          X_df.index = np.arange(len(X_df)).astype(str)
      
          rf = RandomForestRegressor(n_estimators=5, max_depth=3, random_state=0)
          rf.fit(X, y)
      
          n_repeats = 3
          importance_array = permutation_importance(
              rf,
              X,
              y,
              n_repeats=n_repeats,
              random_state=0,
              n_jobs=n_jobs,
              max_samples=max_samples,
          )
      
          # First check that the problem is structured enough and that the model is
          # complex enough to not yield trivial, constant importances:
          imp_min = importance_array["importances"].min()
          imp_max = importance_array["importances"].max()
          assert imp_max - imp_min > 0.3
      
          # Now check that importances computed on dataframe matche the values
          # of those computed on the array with the same data.
  >       importance_dataframe = permutation_importance(
              rf,
              X_df,
              y,
              n_repeats=n_repeats,
              random_state=0,
              n_jobs=n_jobs,
              max_samples=max_samples,
          )
  
  ../venv/lib/python3.13/site-packages/sklearn/inspection/tests/test_permutation_importance.py:357: 
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
  ../venv/lib/python3.13/site-packages/sklearn/utils/_param_validation.py:218: in wrapper
      return func(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^
  ../venv/lib/python3.13/site-packages/sklearn/inspection/_permutation_importance.py:288: in permutation_importance
      scores = Parallel(n_jobs=n_jobs)(
  ../venv/lib/python3.13/site-packages/sklearn/utils/parallel.py:91: in __call__
      return super().__call__(iterable_with_config_and_warning_filters)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:2072: in __call__
      return output if self.return_generator else list(output)
                                                  ^^^^^^^^^^^^
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:1682: in _get_outputs
      yield from self._retrieve()
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:1784: in _retrieve
      self._raise_error_fast()
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:1859: in _raise_error_fast
      error_job.get_result(self.timeout)
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:758: in get_result
      return self._return_or_raise()
             ^^^^^^^^^^^^^^^^^^^^^^^
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
  
  self = <joblib.parallel.BatchCompletionCallBack object at 0x7f8c44e4ef90>
  
      def _return_or_raise(self):
          try:
              if self.status == TASK_ERROR:
  >               raise self._result
  E               joblib.externals.loky.process_executor.BrokenProcessPool: A task has failed to un-serialize. Please ensure that the arguments of the function are all picklable.
  
  ../venv/lib/python3.13/site-packages/joblib/parallel.py:773: BrokenProcessPool
```

COMMENT:
The root cause seems to be this:

```
  Traceback (most recent call last):
    File "/tmp/tmp.q3sHOyewIE/venv/lib/python3.13/site-packages/joblib/externals/loky/process_executor.py", line 453, in _process_worker
      call_item = call_queue.get(block=True, timeout=timeout)
    File "/opt/_internal/cpython-3.13.8/lib/python3.13/multiprocessing/queues.py", line 120, in get
      return _ForkingPickler.loads(res)
             ~~~~~~~~~~~~~~~~~~~~~^^^^^
    File "/tmp/tmp.q3sHOyewIE/venv/lib/python3.13/site-packages/pandas/core/arrays/categorical.py", line 1726, in __setstate__
      return super().__setstate__(state)
             ~~~~~~~~~~~~~~~~~~~~^^^^^^^
    File "pandas/_libs/arrays.pyx", line 85, in pandas._libs.arrays.NDArrayBacked.__setstate__
    File "pandas/_libs/arrays.pyx", line 103, in pandas._libs.arrays.NDArrayBacked.__setstate__
  NotImplementedError: (CategoricalDtype(categories=[0.0, 1.0, 2.0], ordered=False, categories_dtype=float64), array([1, 0, 2, 1, 0, 2, 2, 1, 0, 1, 2, 1, 2, 0, 0, 1, 1, 0, 1, 2, 2, 0,
         1, 2, 2, 0, 2, 1, 2, 0, 0, 2, 2, 2, 2, 2, 1, 1, 1, 1, 0, 1, 1, 0,
         1, 0, 1, 1, 1, 2, 1, 0, 1, 0, 2, 0, 1, 1, 2, 1, 1, 1, 0, 0, 0, 2,
         0, 0, 2, 2, 0, 0, 0, 0, 2, 2, 0, 0, 2, 2, 1, 0, 0, 0, 1, 2, 0, 2,
         1, 0, 0, 1, 1, 2, 2, 2, 1, 2, 2, 2], dtype=int8))
```

do we pin the pandas version on this build? Probably not. This might be a regression in pandas.

Labels: Build / CI