Bump sphinx from 8.1.3 to 8.2.1

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 8.1.3 to 8.2.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/v8.2.1/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v8.1.3...v8.2.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

docs/requirements.txt

@@ -7,7 +7,7 @@ git+https://github.com/graphite-project/ceres.git#egg=ceres
 Django<5
 pyparsing>=3.0.6
 alabaster==1.0.0
-Sphinx==8.1.3
+Sphinx==8.2.1
 jinja2<3.2.0
 sphinx_rtd_theme
 urllib3