Bump mkdocs-material from 9.6.18 to 9.6.21

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.6.18 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@9.6.18...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]

poetry.lock

@@ -48,7 +48,7 @@ ruff = "^0.12.11"
 
 [tool.poetry.group.docs.dependencies]
 mkdocs = "^1.6.1"
-mkdocs-material = "^9.6.18"
+mkdocs-material = "^9.6.21"
 mkdocstrings = { version = ">=0.26,<0.31", extras = ["python"] }
 mkdocs-awesome-pages-plugin = "^2.9.3"
 mkdocs-section-index = "^0.3.10"