Bump sphinx-gallery from 0.13.0 to 0.14.0 in /docs

Bumps [sphinx-gallery](https://github.com/sphinx-gallery/sphinx-gallery) from 0.13.0 to 0.14.0.
- [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@v0.13.0...v0.14.0)

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

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

docs/requirements.txt

@@ -2,4 +2,4 @@ ipykernel==6.21.2
 nbsphinx==0.9.2
 pydata-sphinx-theme==0.13.3
 sphinx==7.0.1
-sphinx-gallery==0.13.0
+sphinx-gallery==0.14.0