Bump mkdocs-material from 9.4.7 to 9.4.8 in /docs

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.4.7 to 9.4.8.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.4.7...9.4.8)

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

Signed-off-by: dependabot[bot] <support@github.com>

docs/requirements.txt

@@ -1,4 +1,4 @@
-mkdocs-material==9.4.7
+mkdocs-material==9.4.8
 mkdocs-minify-plugin==0.7.1
 mkdocs-git-revision-date-localized-plugin==1.2.1
 mkdocs-git-committers-plugin-2==1.2.0