Work around linter issue

Dockerfile

@@ -33,7 +33,7 @@ RUN microdnf ${DNF_OPTS} ${DNF_OPTS_ROOT} install --best --assumeyes --nodocs --
     && microdnf ${DNF_OPTS_ROOT} clean all \
     && rm -f /install-root/var/lib/dnf/history*
 
-FROM ${BASE_REGISTRY:-}${BASE_REGISTRY:+/}${BASE_IMAGE}:${BASE_TAG} 
+FROM ${BASE_REGISTRY}/${BASE_IMAGE}:${BASE_TAG} 
 
 ARG MAILROOM_VERSION=0.0.25
 ARG GITLAB_USER=git