build(deps): bump sphinx from 8.2.3 to 9.0.4 in /requirements

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 8.2.3 to 9.0.4.
- [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...v9.0.4)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/requirements_docs.txt

@@ -8,7 +8,7 @@ nbsphinx==0.9.5
 pypandoc==1.15
 pytest-sphinx==0.6.3
 pyvista==0.46.4
-sphinx==8.2.3
+sphinx==9.0.4
 sphinx-copybutton==0.5.2
 sphinx-gallery==0.20.0
 sphinx-jinja==2.0.2