Docs: Fix Sphinx 9 path warning

[b8zhong]

Fix the Sphinx9 warning for documentation building.

Appears to make the warning go away when building locally.

Fixes #830

• I read the contribution guidelines

[cliffburdick]

/build

[cliffburdick]

Hi @b8zhong , it looks like the warning is still happening:

loading translations [en]... done
/usr/local/lib/python3.10/dist-packages/breathe/project.py:116: RemovedInSphinx90Warning: Sphinx 9 will drop support for representing paths as strings. Use "pathlib.Path" or "os.fspath" instead.
  self._default_build_dir = os.path.dirname(app.doctreedir.rstrip(os.sep))
Converting `source_suffix = '.rst'` to `source_suffix = {'.rst': 'restructuredtext'}`.
building [mo]: targets for 0 po files that are out of date
writing output...

[cliffburdick]

/build

[cliffburdick]

/build

[cliffburdick]

Hi @b8zhong , it looks like the Breathe and Sphinx version upgrade fixed this without any other changes. Just to reduce the amount of changes I will close this one, but thanks for looking into it!

[b8zhong]

Thanks for trying the builds! No problem, glad it went away.