deps: update mkdocs-material requirement from >=9.0 to >=9.7.6

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@9.0.0...9.7.6)

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

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

Author: dependabot[bot]

docs/requirements.txt

@@ -1,3 +1,3 @@
 mkdocs>=1.6.1
-mkdocs-material>=9.0
+mkdocs-material>=9.7.6
 pymdown-extensions>=10.21.2