Bump the docs group with 3 updates (#219)

Bumps the docs group with 3 updates: [pydata-sphinx-theme](https://github.com/pydata/pydata-sphinx-theme), [sphinx](https://github.com/sphinx-doc/sphinx) and [sphinx-gallery](https://github.com/sphinx-gallery/sphinx-gallery).


Updates `pydata-sphinx-theme` from 0.15.4 to 0.16.0
- [Release notes](https://github.com/pydata/pydata-sphinx-theme/releases)
- [Changelog](https://github.com/pydata/pydata-sphinx-theme/blob/main/RELEASE.md)
- [Commits](pydata/pydata-sphinx-theme@v0.15.4...v0.16.0)

Updates `sphinx` from 8.0.2 to 8.1.3
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/v8.1.3/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v8.0.2...v8.1.3)

Updates `sphinx-gallery` from 0.17.1 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@v0.17.1...v0.18.0)

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

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

requirements-doc.txt

@@ -1,11 +1,11 @@
 jupyter_sphinx==0.5.3
 jupyterlab==4.3.0
 numpydoc==1.8.0
-pydata-sphinx-theme==0.15.4
+pydata-sphinx-theme==0.16.0
 pyvista==0.44.1
-sphinx==8.0.2
+sphinx==8.1.3
 sphinx-design==0.6.1
-sphinx-gallery==0.17.1
+sphinx-gallery==0.18.0
 trame==3.7.0
 trame-vtk==2.8.11
 trame-vuetify==2.7.1