build: include annotations in the multi-arch images

This needs --annotations support in buildx which was introduced in
Docker buildx 0.12.0.

.github/bin/get-buildx-args

@@ -11,6 +11,10 @@ else
     done
 fi
 
+# Expose annotations
+WEBLATE_VERSION=$(sed -n 's/^ENV WEBLATE_VERSION \(.*\)/\1/p' Dockerfile)
+sed -n "s/^LABEL \(org.opencontainers.image.*\)/--annotation \1/p" Dockerfile | sed "s/\\\$WEBLATE_VERSION/$WEBLATE_VERSION/"
+
 # Write to local cache unless publishing (not compatible with push)
 if [ "$1" != "publish" ] ; then
     echo --cache-to "type=local,dest=/tmp/.buildx-cache/$MATRIX_ARCHITECTURE,mode=max"