Bump sphinx from 8.2.1 to 8.2.3 in /backend/docs

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 8.2.1 to 8.2.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v8.2.1...v8.2.3)

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

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

backend/docs/requirements.txt

@@ -1,6 +1,6 @@
 ipython==8.32.0
 myst_parser==4.0.1
 nbsphinx==0.9.6
-sphinx==8.2.1
+sphinx==8.2.3
 sphinx-copybutton==0.5.2
 sphinx-rtd-theme==3.0.2