build(deps): bump sphinx from 8.0.2 to 8.1.3 in /docs

Bumps [sphinx](https:/sphinx-doc/sphinx) from 8.0.2 to 8.1.3.
- [Release notes](https:/sphinx-doc/sphinx/releases)
- [Changelog](https:/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v8.0.2...v8.1.3)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

docs/requirements.txt

@@ -1,4 +1,4 @@
-sphinx==8.0.2
+sphinx==8.1.3
 furo==2024.8.6
 sphinx-autodoc-typehints==2.3.0
 kloppy==3.15.0