Bump sphinx from 1.8.6 to 7.2.1

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 1.8.6 to 7.2.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES)
- [Commits](sphinx-doc/sphinx@v1.8.6...v7.2.1)

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

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

docs/requirements.txt

@@ -1,5 +1,5 @@
 urllib3==1.26.15 # https://github.com/readthedocs/readthedocs.org/issues/10290
-sphinx==1.8.6
+sphinx==7.2.1
 sphinx-rtd-theme==1.2.0
 sphinxcontrib-napoleon==0.7
 invoke==2.0.0