Bump sphinx from 7.2.6 to 7.3.7 in /docs (#4322)

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 7.2.6 to 7.3.7.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v7.2.6...v7.3.7)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docs/requirements.txt

@@ -1,7 +1,7 @@
 # Used by ReadTheDocs; pinned requirements for stability.
 
 myst-parser==2.0.0
-Sphinx==7.2.6
+Sphinx==7.3.7
 # Older versions break Sphinx even though they're declared to be supported.
 docutils==0.20.1
 sphinxcontrib-programoutput==0.17