CI: (deps): Bump sphinx from 4.5.0 to 6.1.3 in /ci

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 4.5.0 to 6.1.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES)
- [Commits](sphinx-doc/sphinx@v4.5.0...v6.1.3)

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

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

Author: dependabot[bot]

ci/doc_requirements.txt

@@ -1,4 +1,4 @@
-sphinx==4.5.0
+sphinx==6.1.3
 pydata-sphinx-theme==0.8.1
 sphinx-gallery==0.11.1
 myst-parser==0.18.1