⬆ Bump mkdocs-material from 9.1.17 to 9.1.21

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.1.17 to 9.1.21.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.1.17...9.1.21)

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

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

requirements-docs.txt

@@ -1,5 +1,5 @@
 -e .
-mkdocs-material==9.1.17
+mkdocs-material==9.1.21
 mdx-include >=1.4.1,<2.0.0
 mkdocs-markdownextradata-plugin >=0.1.7,<0.3.0
 typer-cli >=0.0.13,<0.0.14