Update sphinx requirement from <5.1.2,>=1.8.1 to >=1.8.1,<7.2.7

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/master/CHANGES)
- [Commits](sphinx-doc/sphinx@v1.8.1...v7.2.6)

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

Signed-off-by: dependabot[bot] <support@github.com>

requirements-dev.txt

@@ -6,7 +6,7 @@ pytest==7.3.2
 pytest-cov==4.1.0
 pytest-sugar==0.9.7
 PyMySQL==1.0.3
-sphinx>=1.8.1, <5.1.2
+sphinx>=1.8.1, <7.2.7
 sphinxcontrib-asyncio==0.3.0
 SQLAlchemy==1.3.24
 uvloop==0.17.0