Bump mkdocs-material from 9.1.6 to 9.1.20

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.1.6 to 9.1.20.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.1.6...9.1.20)

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

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