Bump sphinx from 8.1.0 to 8.1.3

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 8.1.0 to 8.1.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v8.1.0...v8.1.3)

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

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

doc/requirements.txt

@@ -1,7 +1,7 @@
 click==8.1.7
 entrypoints==0.4
 Pillow==10.4.0
-Sphinx==8.1.0
+Sphinx==8.1.3
 furo==2024.8.6
 ipython==8.28.0
 netCDF4==1.7.1.post2