Bump sphinx from 5.0.1 to 5.1.1 in /requirements

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 5.0.1 to 5.1.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/5.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v5.0.1...v5.1.1)

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

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

Author: dependabot[bot]

requirements/docs.txt

@@ -1 +1 @@
-Sphinx==5.0.1
+Sphinx==5.1.1