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:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

dev_requirements.txt

@@ -3,7 +3,7 @@ black==25.1.0
 isort==6.0.1
 pyright==1.1.403
 mypy==1.17.0
-mkdocs-material==9.6.16
+mkdocs-material==9.6.21
 mkdocstrings==0.30.0
 mkdocstrings[python]==0.30.0
 pytest==8.4.1