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

Updates the requirements on [mkdocs](https://github.com/mkdocs/mkdocs) to permit the latest version.
- [Release notes](https://github.com/mkdocs/mkdocs/releases)
- [Commits](mkdocs/mkdocs@1.5.3...1.6.0)

---
updated-dependencies:
- dependency-name: mkdocs
  dependency-type: direct:development
...

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

gh-pages/requirements-dev.txt

@@ -1,4 +1,4 @@
-mkdocs~=1.5.3
+mkdocs~=1.6.0
 mkdocs-awesome-pages-plugin~=2.9.2
 mkdocs-material~=9.5.17
 mkdocs-git-revision-date-plugin~=0.3.2