CI: (deps): Bump sphinx from 8.1.3 to 9.0.4 in /ci-dev

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 8.1.3 to 9.0.4.
- [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@v8.1.3...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]

ci-dev/doc_requirements.txt

@@ -1,4 +1,4 @@
-sphinx==8.1.3
+sphinx==9.0.4
 pydata-sphinx-theme==0.16.1
 sphinx-design==0.6.1
 sphinx-gallery==0.20.0