`_GenericAlias` caches origin's `__module__`

Bug report

Bug description:

When subscripting a class, __module__ gets saved. This prevents fixing it up later:

https://github.com/python/cpython/blob/4c3f0cbeaec0d49212d305618743fabb0e74a696/Lib/typing.py#L1411

from typing import Generic, TypeVar
T = TypeVar("T")

class A(Generic[T]):
  pass

x = A[T]  # this originally was in ... somewhere, but is here for minimization
A.__module__ = "new_module"
assert x.__module__ == "new_module"  # this is going to raise AssertionError

This came up when updating the Sphinx version in trio due to our handling of private/public. We update __module__ for these classes in __init__ (to make Sphinx work, among other things) but this doesn't end up updating any stored _GenericAliass' __module__s.

CPython versions tested on:

3.11

Operating systems tested on:

Windows

從 Lib/typing.py 中連結的 _GenericAlias 實作開始，並在 Python 3.11 上重現回報的 A[T] 範例。追蹤如何取得 alias 的 module，然後驗證變更 A.module 會反映到 alias 中，同時不會破壞 typing 的既有行為。