build(deps-dev): bump mkdocs-material from 9.6.1 to 9.6.9

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.6.1 to 9.6.9.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.6.1...9.6.9)

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

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

Author: dependabot[bot]