use newer mkdocs

Dockerfile.debian-bullseye-mkdocs

@@ -2,7 +2,7 @@ FROM debian:bullseye
 
 RUN apt-get -qq update && \
     apt-get -qq dist-upgrade && \
-    apt-get -qq install mkdocs python3-pip && \
+    apt-get -qq install python3-pip && \
     apt-get -qq clean
 
-RUN pip3 install mkdocs-static-i18n
+RUN pip3 install mkdocs mkdocs-static-i18n