feat: make Dockerfile syntax checker stricter (error=true)

containers/debian/Dockerfile

 #syntax=docker/dockerfile:1.8
-#check
+#check=error=true
 ARG BASE_IMAGE="amd64/debian:stable-slim"
 ARG BUILD_IMAGE="debian_stable_base"
 

containers/eic/Dockerfile

 #syntax=docker/dockerfile:1.10
-#check
+#check=error=true
 ARG DOCKER_REGISTRY="eicweb/"
 ARG BUILDER_IMAGE="debian_stable_base"
 ARG RUNTIME_IMAGE="debian_stable_base"