Bump sphinx from 5.1.1 to 5.2.1 (#355)

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 5.1.1 to 5.2.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/5.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v5.1.1...v5.2.1)

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

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

docs/requirements.txt

@@ -1,3 +1,3 @@
-sphinx==5.1.1
+sphinx==5.2.1
 sphinx_rtd_theme==1.0.0
 m2r2==0.3.2