MNT: (deps): Bump sphinx-gallery from 0.11.1 to 0.18.0 in /ci

Bumps [sphinx-gallery](https://github.com/sphinx-gallery/sphinx-gallery) from 0.11.1 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@v0.11.1...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

@@ -4,6 +4,6 @@ metpy==1.6.3
 pint==0.19
 sphinx==5.2.3
 sphinx_rtd_theme==1.0.0
-sphinx-gallery==0.11.1
+sphinx-gallery==0.18.0
 myst-parser==0.18.1
 netCDF4==1.7.2