Bump sphinx in /docs in the docs group across 1 directory

Bumps the docs group with 1 update in the /docs directory: [sphinx](https://github.com/sphinx-doc/sphinx).


Updates `sphinx` from 7.4.7 to 8.1.3
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/v8.1.3/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v7.4.7...v8.1.3)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: docs
...

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

docs/requirements.txt

@@ -1,6 +1,6 @@
 Pillow==10.0.1
 PyYAML==6.0.1
-Sphinx==7.4.7
+Sphinx==8.1.3
 conda-sphinx-theme==0.2.2
 linkify-it-py==2.0.2
 myst-parser==2.0.0