Lock mkdocs-material to version 6.2.8 to meet mkdocs version in docker image

docker-compose.yml

@@ -9,7 +9,7 @@ services:
       - 8999:8000
     environment:
       LIVE_RELOAD_SUPPORT: 'true'
-      ADD_MODULES: fontawesome-markdown mkdocs-git-revision-date-localized-plugin mkdocs-material mkdocs-build-plantuml-plugin mkdocs-new-features-notifier mkdocs-git-authors-plugin git+https://github.com/jldiaz/mkdocs-plugin-tags.git
+      ADD_MODULES: fontawesome-markdown mkdocs-git-revision-date-localized-plugin mkdocs-material==6.2.8 mkdocs-build-plantuml-plugin mkdocs-new-features-notifier mkdocs-git-authors-plugin git+https://github.com/jldiaz/mkdocs-plugin-tags.git
       FAST_MODE: 'true'
       DOCS_DIRECTORY: /mkdocs
     volumes: