Update sphinx requirement from <5.1.1,>=1.8.1 to >=1.8.1,<5.1.2 (#829)

Updates the requirements on [sphinx](https://github.com/sphinx-doc/sphinx) to permit the latest version.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/5.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v1.8.1...v5.1.1)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:development
...

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

requirements-dev.txt

@@ -5,7 +5,7 @@ pytest==7.1.2
 pytest-cov==3.0.0
 pytest-sugar==0.9.5
 PyMySQL==1.0.2
-sphinx>=1.8.1, <5.1.1
+sphinx>=1.8.1, <5.1.2
 sphinxcontrib-asyncio==0.3.0
 SQLAlchemy==1.3.24
 uvloop==0.16.0; python_version < '3.11'