chore(deps): update mkdocs-material requirement in /docs

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...9.7.7)

---
updated-dependencies:
- dependency-name: mkdocs-material
  dependency-version: 9.7.7
  dependency-type: direct:production
...

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

Author: dependabot[bot]

docs/requirements.txt

@@ -9,5 +9,5 @@
 # `mkdocs serve` locally.
 
 mkdocs>=1.6
-mkdocs-material>=9.5
+mkdocs-material>=9.7.7
 pymdown-extensions>=10.7