_StrPath is dead; long live _StrPath

[AA-Turner]

Closes #12686.

[smithdc1]

Should this say Sphinx 9?

[AA-Turner]

Thanks, done in 46ce447.

A

[jfbu]

ping @AA-Turner with this commit I started seeing

copying static files... /Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/filecmp.py:62: RemovedInSphinx90Warning: Sphinx 8 will drop support for representing paths as strings. Use "pathlib.Path" or "os.fspath" instead.
  outcome = _cache.get((f1, f2, s1, s2))

when building our own html docs. I could not identify where the last line comes from, I thought a remnant of some debugging or may some doctest (but this commit did not touch doc/)

Python version: 3.12.3 (CPython)
Docutils version: 0.20.1 
Pygments version: 2.18.0
Jinja2 version: 3.1.4

With 8.0.0rc1 I only see

copying static files... done
copying extra files... done

[AA-Turner]

#12708 hopefully fixes this.

A