ci: doc: bump sphinx from 8.1.3 to 8.2.3 in /doc in the doc-deps group

Bumps the doc-deps group in /doc with 1 update: [sphinx](https://github.com/sphinx-doc/sphinx).

Updates `sphinx` from 8.1.3 to 8.2.3
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](https://github.com/sphinx-doc/sphinx/compare/v8.1.3...v8.2.3

)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: doc-deps
...

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>