update to_py_obj to support np.number
Author: PrettyMeng
Pull request: yes

# What does this PR do?
Update `to_py_obj` function to make it support np.number type.

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Fixes # See an example below:

>>> tokenizer.decode(110)
'no'
>>> tokenizer.decode(np.array([110])[0])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/prettymeng/anaconda3/envs/ptuning/lib/python3.8/site-packages/transformers/tokenization_utils_base.py", line 3179, in decode
    return self._decode(
  File "/Users/prettymeng/anaconda3/envs/ptuning/lib/python3.8/site-packages/transformers/tokenization_utils_fast.py", line 527, in _decode
    text = self._tokenizer.decode(token_ids, skip_special_tokens=skip_special_tokens)
TypeError: Can't convert 110 to Sequence


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Comments:
@sgugger Hi! This is an reopened PR for #14041, could you please check whether the failed tests are related to my PR?

All good, thanks a lot for your contribution!