Bump mkdocs-material from 8.5.7 to 9.1.5 (#666)

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 8.5.7 to 9.1.5.
- [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@8.5.7...9.1.5)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -6,7 +6,7 @@ trio==0.21.0
 # Docs
 mkdocs==1.4.2
 mkdocs-autorefs==0.3.1
-mkdocs-material==8.5.7
+mkdocs-material==9.1.5
 mkdocs-material-extensions==1.1.1
 mkdocstrings[python-legacy]==0.19.1
 jinja2==3.1.2