[Python 3.9 compat] Check for __class_getitem__

[JulienPalard]

Python 3.9 starts to make a great use of __class_getitem__ for exemple in collections.deque.

pylint/checkers/typecheck.py should probably look for it to infer if something is subscriptable.

Reproducer:

import collections
print(collections.deque[int])

which give:

test.py:11:6: E1136: Value 'collections.deque' is unsubscriptable (unsubscriptable-object)

while the code works thanks to the __class_getitem__.

Related to #3890.
See also #3882.

[hippo91]

👍

[cdce8p]

This seems to be fixed with: pylint-dev/astroid#885
So non blocker after an astroid update 🎉

[hippo91]

@cdce8p 👍