CI: (deps): Bump sphinx from 6.2.1 to 7.1.1 in /ci

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 6.2.1 to 7.1.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES)
- [Commits](sphinx-doc/sphinx@v6.2.1...v7.1.1)

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

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

ci/doc_requirements.txt

@@ -1,4 +1,4 @@
-sphinx==6.2.1
+sphinx==7.1.1
 pydata-sphinx-theme==0.13.3
 sphinx-design==0.4.1
 sphinx-gallery==0.13.0