Update sphinx requirement from ~=8.2.3 to ~=9.1.0 in the pip group

Updates the requirements on [sphinx](https://github.com/sphinx-doc/sphinx) to permit the latest version.

Updates `sphinx` to 9.1.0
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v8.2.3...v9.1.0)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-version: 9.1.0
  dependency-type: direct:production
  dependency-group: pip
...

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

Author: dependabot[bot]

requirements.txt

@@ -7,4 +7,4 @@ sphinx-notfound-page>=1.0.0
 sphinx_copybutton>=0.3.3
 sphinxext-opengraph>=0.13.0
 sphinxext-rediraffe
-Sphinx~=8.2.3
+Sphinx~=9.1.0