Bump mkdocs-material from 9.6.20 to 9.6.21

Bumps [mkdocs-material](https://github.com/squidfunk/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:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

poetry.lock

@@ -23,7 +23,7 @@ invoke = "^2.2.0"
 mdx_truly_sane_lists = "^1.3"
 mike = "^2.1.3"
 mkdocs = "^1.5.3"
-mkdocs-material = "^9.6.20"
+mkdocs-material = "^9.6.21"
 pep8-naming = "^0.15.1"
 pytest = "^8.4.2"
 python-dateutil = "^2.9.0"