fix(deps): bump sphinx-gallery from 0.14.0 to 0.15.0

Bumps [sphinx-gallery](https://github.com/sphinx-gallery/sphinx-gallery) from 0.14.0 to 0.15.0.
- [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@v0.14.0...v0.15.0)

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

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

Author: dependabot[bot]

requirements-docs.txt

@@ -1,5 +1,5 @@
 matplotlib==3.8.0
 numpydoc==1.6.0
 sphinx==7.2.5
-sphinx-gallery==0.14.0
+sphinx-gallery==0.15.0
 sphinx-rtd-theme==1.3.0