Update sphinx requirement from <9.0.5 to <9.1.1

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@v3.5.0...v9.1.0)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-version: 9.1.0
  dependency-type: direct:development
...

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

Author: dependabot[bot]

setup.cfg

@@ -53,7 +53,7 @@ docs =
 	# upstream
 	sphinx >= 3.5
 	# workaround for sphinx/sphinx-doc#11662
-	sphinx < 9.0.5
+	sphinx < 9.1.1
 	jaraco.packaging >= 9.3
 	rst.linker >= 1.9
 	furo