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] <support@github.com>

pyproject.toml

@@ -101,7 +101,7 @@ doc = [
     "sphinx-autobuild==2021.3.14",
     "sphinx-autodoc-typehints==1.25.2",
     "sphinx-copybutton==0.5.2",
-    "sphinx-gallery==0.14.0",
+    "sphinx-gallery==0.15.0",
     "sphinxcontrib-websupport==1.2.6",
     "sphinxemoji==0.2.0",
     "sphinx-reredirects==0.1.3",