Replace != None with is not None in Python bindings

[stephane-caron]

In Python it is better to compare to not None (typo fixed, thanks @nim65s) with is or is not rather than == and != (e.g. the comparison operators may not be defined).

In this code it changes nothing, because tensors are from PyTorch:

In [1]: import torch

In [2]: x = torch.tensor([1, 2, 3])

In [3]: x is not None
Out[3]: True

In [4]: x != None
Out[4]: True

But with NumPy arrays it would yield, for instance:

In [1]: x = np.array([1, 2, 3])

In [2]: x is not None
Out[2]: True

In [3]: x != None
Out[3]: array([ True,  True,  True])

In [4]: if x != None:
   ...:     pass
   ...: 
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[4], line 1
----> 1 if x != None:
      2     pass

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

[hrp2-14]

Hi ! This project doesn't usually accept pull requests on the main branch.
If this wasn't intentionnal, you can change the base branch of this PR to devel
(No need to close it for that). Best, a bot.

[nim65s]

This should have been found by some linter :)

NB: typo: not -> None