[PR #12744/c947145f backport][8.3.x] Replaced typing.Self with typing_extensions.Self

[patchback]

This is a backport of PR #12744 as merged into main (c947145).

Fixes #11916 (comment)

Importing Self from typing breaks the return type on Python 3.9 and under. You should be using from typing_extension import Self instead.

For example, the following code:

def pytest_collect_file(file_path: pathlib.Path, parent: Node) -> CheckdocsItem | None:
    if file_path.name not in project_files:
        return None
    return CheckdocsItem.from_parent(parent, name='project')

Will error with Returning Any from function declared to return "CheckdocsItem | None" [no-any-return] on 3.8 & 3.9, but pass on 3.10+ Which can only be worked around by disabling the error entirely in mypy, or doing:

def pytest_collect_file(file_path: pathlib.Path, parent: Node) -> CheckdocsItem | None:
    if file_path.name not in project_files:
        return None
    if sys.version_info >= (3, 10):
        return CheckdocsItem.from_parent(parent, name='project')
    else:
        return cast(CheckdocsItem, CheckdocsItem.from_parent(parent, name='project'))

[nicoddemus]

I had to cherry-pick several commits regarding pre-commit version updates and type-checking fixes.

[nicoddemus]

I will not merge myself, would like a second set of eyes to take a look and merge. 👍

[Pierre-Sassoulas]

LGTM, everything is either automated or a cherry-picking it seems (so if the CI is green there's probably no issues with it). Not sure if I we should merge or squash though.

[nicoddemus]

In this case I think merging is appropriate, so the cherry-picked commits are preserved. 👍