Sphinx 7.2 dropped support for Python 3.8

[freakboy3742]

Describe the bug

Sphinx 7.2 dropped support for Python 3.8. Documentation builds on Python 3.8 will now fail.

This won't affect CI, but it might affect users building locally.

Steps to reproduce

tox -r -e docs in a Python 3.8 environment.

Expected behavior

The tox docs target should build without error on Python 3.8

Screenshots

No response

Environment

• Python version: 3.8

Logs

Additional context

The fix for this is to add a Python version qualifier to the docs extra dependencies in setup.cfg.