Bump mkdocs-material from 8.5.3 to 8.5.6 in /config (#88)

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 8.5.3 to 8.5.6.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@8.5.3...8.5.6)

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

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Author: dependabot[bot]

config/requirements.txt

@@ -1,6 +1,6 @@
 mkdocs==1.4.0
 mkdocs-exclude==1.0.2
-mkdocs-material==8.5.3
+mkdocs-material==8.5.6
 mkdocs-minify-plugin==0.5.0
 #mkdocs-drawio-exporter
 mkdocs-git-revision-date-localized-plugin==1.1.0