CLI test command throws NonMatchingSplitsSizesError when saving infos
When trying to generate a datset JSON metadata, a `NonMatchingSplitsSizesError` is thrown:
```
$ datasets-cli test datasets/arabic_billion_words --save_infos --all_configs
Testing builder 'Alittihad' (1/10)
Downloading and preparing dataset arabic_billion_words/Alittihad (download: 332.13 MiB, generated: Unknown size, post-processed: Unknown size, total: 332.13 MiB) to .cache\arabic_billion_words\Alittihad\1.1.0\8175ff1c9714c6d5d15b1141b6042e5edf048276bb81a9c14e35e149a7a62ae4...
Traceback (most recent call last):
  File "path\huggingface\datasets\.venv\Scripts\datasets-cli-script.py", line 33, in <module>
    sys.exit(load_entry_point('datasets', 'console_scripts', 'datasets-cli')())
  File "path\huggingface\datasets\src\datasets\commands\datasets_cli.py", line 33, in main
    service.run()
  File "path\huggingface\datasets\src\datasets\commands\test.py", line 144, in run
    builder.download_and_prepare(
  File "path\huggingface\datasets\src\datasets\builder.py", line 607, in download_and_prepare
    self._download_and_prepare(
  File "path\huggingface\datasets\src\datasets\builder.py", line 709, in _download_and_prepare
    verify_splits(self.info.splits, split_dict)
  File "path\huggingface\datasets\src\datasets\utils\info_utils.py", line 74, in verify_splits
    raise NonMatchingSplitsSizesError(str(bad_splits))
datasets.utils.info_utils.NonMatchingSplitsSizesError: [{'expected': SplitInfo(name='train', num_bytes=0, num_examples=0, dataset_name='arabic_billion_words'), 'recorded': SplitInfo(name='train', num_bytes=1601790302, num_examples=349342, dataset_name='arabic_billion_words')}]
```

This is due because a previous run generated a wrong `dataset_info.json`.

This error can be avoided by passing `--ignore_verifications`, but I think this should be assumed when passing `--save_infos`.