Update sphinx requirement from ^6.0.0 to >=6,<8

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.rst)
- [Commits](sphinx-doc/sphinx@v6.0.0...v7.1.2)

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

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

pyproject.toml

@@ -73,7 +73,7 @@ urllib3 = ">=1.22.0,<3"
 optional = true
 
 [tool.poetry.group.docs.dependencies]
-sphinx = "^6.0.0"
+sphinx = ">=6,<8"
 sphinx-rtd-theme = ">=1.3,<3.0"
 certifi = ">=2018.4.16"
 expiringdict = ">=1.1.4"