⬆ Update mkdocs-material requirement (#330)

Updates the requirements on [mkdocs-material](https://github.com/squidfunk/mkdocs-material) to permit the latest version.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@8.1.4...9.0.0)

---
updated-dependencies:
- dependency-name: mkdocs-material
  dependency-type: direct:production
...

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pyproject.toml

@@ -75,7 +75,7 @@ test = [
 ]
 docs = [
     "mkdocs >=1.1.2,<2.0.0",
-    "mkdocs-material >=8.1.4,<9.0.0",
+    "mkdocs-material >=8.1.4,<10.0.0",
     "mdx-include >=1.4.1,<2.0.0",
     "mkdocs-markdownextradata-plugin >=0.1.7,<0.3.0",
     "mkdocs-mermaid2-plugin==0.6.0",