Bump sphinx from 4.2.0 to 4.3.0 (#6294)

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 4.2.0 to 4.3.0.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/4.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v4.2.0...v4.3.0)

---
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>

requirements/doc.txt

@@ -2,7 +2,7 @@ aiohttp-theme==0.1.6
 # Temp fix till updated: https://github.com/blockdiag/blockdiag/pull/148
 funcparserlib==1.0.0a0
 pygments==2.10.0
-sphinx==4.2.0
+sphinx==4.3.0
 sphinxcontrib-asyncio==0.3.0
 sphinxcontrib-blockdiag==2.0.0
 sphinxcontrib-towncrier==0.2.0a0