Bump mkdocs-material from 9.5.38 to 9.5.40 (kubeflow#1166)

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.5.38 to 9.5.40.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.5.38...9.5.40)

---
updated-dependencies:
- dependency-name: mkdocs-material
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

docs/requirements.txt

@@ -1 +1 @@
-mkdocs-material == 9.5.38
+mkdocs-material == 9.5.40