chore(deps-dev): update mkdocs-material requirement in /gh-pages

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/docs/changelog.md)
- [Commits](squidfunk/mkdocs-material@7.0.3...7.0.6)

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

gh-pages/requirements-dev.txt

@@ -1,4 +1,4 @@
 mkdocs~=1.1.2
 mkdocs-awesome-pages-plugin~=2.5.0
-mkdocs-material~=7.0.3
+mkdocs-material~=7.0.6
 mkdocs-git-revision-date-plugin~=0.3.1