chore(deps)(deps): update sphinx requirement

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/v9.0.4/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v5.0.0...v9.0.4)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-version: 9.0.4
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements-doc.txt

@@ -6,7 +6,7 @@ numba
 # document requirements
 pandoc
 Jinja2
-sphinx>=5, <8.2.0
+sphinx>=5, <9.1.0
 myst-nb
 sphinx_thebe
 sphinx-autodoc-typehints