Bump sphinx-gallery from 0.11.1 to 0.12.2 in /requirements (#226)

Bumps [sphinx-gallery](https://github.com/sphinx-gallery/sphinx-gallery) from 0.11.1 to 0.12.2.
- [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...v0.12.2)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/requirements_docs.txt

@@ -4,6 +4,6 @@ notfound==1.0.2
 pypandoc==1.11
 pyvista==0.38.3
 sphinx-copybutton==0.5.1
-sphinx-gallery==0.11.1
+sphinx-gallery==0.12.2
 sphinx-notfound-page==0.8.3
 vtk==9.2.6