deps: update mkdocs-material requirement from >=9.5 to >=9.7.6 (#42)

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@9.5.0...9.7.6)

---
updated-dependencies:
- dependency-name: mkdocs-material
  dependency-version: 9.7.6
  dependency-type: direct:production
...

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Author: dependabot[bot]

docs/requirements-docs.txt

@@ -1 +1 @@
-mkdocs-material>=9.5
+mkdocs-material>=9.7.6