build(deps): bump mkdocs-material from 8.5.4 to 8.5.6

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 8.5.4 to 8.5.6.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](https://github.com/squidfunk/mkdocs-material/compare/8.5.4...8.5.6)

---
updated-dependencies:
- dependency-name: mkdocs-material
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

docs/requirements.txt

@@ -2,7 +2,7 @@ lightgallery==0.5
 mkdocs-awesome-pages-plugin==2.8.0
 mkdocs-git-revision-date-localized-plugin==1.1.0
 mkdocs-macros-plugin==0.7.0
-mkdocs-material==8.5.4
+mkdocs-material==8.5.6
 mkdocs-minify-plugin==0.5.0
 mkdocs-redirects==1.2.0
 mkdocs-include-markdown-plugin==3.8.0