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>

Author: dependabot[bot]

pyproject.toml

@@ -66,7 +66,7 @@ dev = [
   "mypy==v1.4.1 ; python_version>='3.7' and python_version<'3.8'",
   "mypy==v1.14.1 ; python_version>='3.8'",
   # Docs.
-  "Sphinx==8.1.3 ; python_version>='3.11'",
+  "Sphinx==8.2.1 ; python_version>='3.11'",
   "sphinx-rtd-theme==3.0.2 ; python_version>='3.11'",
   "myst-parser==4.0.0 ; python_version>='3.11'",
   # Packaging.