Bump mkdocs-material from 8.4.0 to 9.1.1

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 8.4.0 to 9.1.1.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Upgrade guide](https://github.com/squidfunk/mkdocs-material/blob/master/docs/upgrade.md)
- [Commits](squidfunk/mkdocs-material@8.4.0...9.1.1)

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

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

requirements-docs.txt

@@ -1,4 +1,4 @@
-mkdocs-material==8.4.0
+mkdocs-material==9.1.1
 plotly==4.14.3
 mkdocstrings==0.19.0
 mkdocstrings-python==0.7.1