Bump mkdocs-material from 5.5.0 to 5.5.1

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 5.5.0 to 5.5.1.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/docs/changelog.md)
- [Commits](https://github.com/squidfunk/mkdocs-material/compare/5.5.0...5.5.1)

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

docs/requirements-docs.txt

@@ -1,2 +1,2 @@
-mkdocs-material==5.5.0
+mkdocs-material==5.5.1
 mdx_truly_sane_lists==1.2