Bumps the doc-dependencies group with 3 updates in the / directory: [ansys-sphinx-theme](https://github.com/ansys/ansys-sphinx-theme), [sphinx](https://github.com/sphinx-doc/sphinx) and [sphinx-gallery](https://github.com/sphinx-gallery/sphinx-gallery).


Updates `ansys-sphinx-theme` from 1.1.2 to 1.1.6
- [Release notes](https://github.com/ansys/ansys-sphinx-theme/releases)
- [Commits](ansys/ansys-sphinx-theme@v1.1.2...v1.1.6)

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: ansys-sphinx-theme
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: doc-dependencies
- dependency-name: sphinx
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: doc-dependencies
- dependency-name: sphinx-gallery
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: doc-dependencies
...

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