chore(deps): bump mkdocs-material in the python-packages group

Bumps the python-packages group with 1 update: [mkdocs-material](https://github.com/squidfunk/mkdocs-material).

Updates `mkdocs-material` from 9.6.20 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@9.6.20...9.6.21)

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

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

Author: dependabot[bot]

mkdocs-requirements.txt

@@ -1,5 +1,5 @@
 mkdocs-git-revision-date-localized-plugin==1.4.7
-mkdocs-material==9.6.20
+mkdocs-material==9.6.21
 mkdocs==1.6.1
 mkdocs-redirects==1.2.2
 pygments==2.19.2