Dependencies: Bump mkdocs-material from 9.1.21 to 9.2.8 (#456)

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.1.21 to 9.2.8.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.1.21...9.2.8)

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

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

requirements.txt

@@ -2,5 +2,5 @@
 # To install them all run 'pip install -r requirements.txt' in the same directory
 
 mkdocs == 1.5.2
-mkdocs-material == 9.1.21
+mkdocs-material == 9.2.8
 mkdocs-redirects == 1.2.1