Bump mkdocs-material from 9.6.16 to 9.6.21

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.6.16 to 9.6.21.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.6.16...9.6.21)

---
updated-dependencies:
- dependency-name: mkdocs-material
  dependency-version: 9.6.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

requirements.txt

@@ -2,6 +2,6 @@ Markdown==3.9
 mike==2.1.3
 mkdocs-git-revision-date-plugin==0.3.2
 mkdocs-macros-plugin==1.4.0 
-mkdocs-material==9.6.16
+mkdocs-material==9.6.21
 mkdocs==1.6.1
 setuptools==80.9.0