Bump sphinx from 5.0.2 to 5.1.1 in /api (#837)

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 5.0.2 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@v5.0.2...v5.1.1)

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

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

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