Bump sphinx from 3.5.4 to 7.0.1

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.5.4 to 7.0.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.5.4...v7.0.1)

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

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

docs/requirements.txt

@@ -1,4 +1,4 @@
-sphinx==3.5.4
+sphinx==7.0.1
 pangeo-sphinx-book-theme==0.2
 myst-parser==0.13.6
 myst-nb==0.12.3