Bump mkdocs-material from 8.1.8 to 8.1.9 (#32)

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 8.1.8 to 8.1.9.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@8.1.8...8.1.9)

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

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

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

requirements.dev.txt

@@ -8,7 +8,7 @@ codecov
 pytest-cov
 mkdocs == 1.2.3
 mkdocs-markdownextradata-plugin == 0.2.5
-mkdocs-material == 8.1.8
+mkdocs-material == 8.1.9
 mkdocs-mermaid2-plugin
 markdown-include
 pymdown-extensions