[autodoc] Fix subclassing a MockObject together with typing.Generic

[Daraan]

Purpose

When subclassing a MockObject and typing.Generic the mock object will be detected as a TypeVar by typing when subclassing Generic, see: https://github.com/python/cpython/blob/31d3836f26096f9503ca68f4e89d927bc1e060cd/Lib/typing.py#L1175

Especially this line in the utility function to gather TypeVars should not be True: elif hasattr(t, '__typing_subst__'):.
But, as it is a mock object, hasattr will return True which will raise an error on Python 3.11/12. (3.10 is fine). I did not test 3.13 or 3.14.

References

Fixes #12797
Continues PR #12850 by @IkorJefocur with a slight reinterpretation and added tests.

[Daraan]

I'll appreciate input on the failing Docutils HEAD and LaTeX tests if they are relevant and how to address them.

[jfbu]

I relaunched the failed Docutils HEAD test and it now passes with current Docutils revision. LaTeX failure was only a duplicate because it uses Docutils HEAD since some time.

See #13845 (comment) and #13845 (comment) for context.

[Daraan]

I relaunched the failed Docutils HEAD test and it now passes with current Docutils revision. LaTeX failure was only a duplicate because it uses Docutils HEAD since some time.

See #13845 (comment) and #13845 (comment) for context.

Thanks for the notice. Mind to do a review :) ?