CI: (deps): Bump sphinx-gallery from 0.17.1 to 0.18.0 in /ci

Bumps [sphinx-gallery](https://github.com/sphinx-gallery/sphinx-gallery) from 0.17.1 to 0.18.0.
- [Release notes](https://github.com/sphinx-gallery/sphinx-gallery/releases)
- [Changelog](https://github.com/sphinx-gallery/sphinx-gallery/blob/master/.github_changelog_generator)
- [Commits](sphinx-gallery/sphinx-gallery@v0.17.1...v0.18.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

ci/doc_requirements.txt

@@ -1,7 +1,7 @@
 sphinx==8.1.3
 pydata-sphinx-theme==0.15.4
 sphinx-design==0.6.1
-sphinx-gallery==0.17.1
+sphinx-gallery==0.18.0
 myst-parser==4.0.0
 netCDF4==1.7.1
 geopandas==1.0.1