Revert "Drop brackets"

This reverts commit 4319baa7b59daf80405e49c5ab52413029359495.

Dockerfile

@@ -11,11 +11,11 @@ ENV EXTRA_VARS=""
 FROM builder AS netbootxyz-production
 ENV EXTRA_VARS="--extra-vars @script/netbootxyz-overrides.yml"
 
-FROM netbootxyz-$NBXYZ_OVERRIDES as final
+FROM netbootxyz-${NBXYZ_OVERRIDES} as final
 RUN \
   echo "**** running ansible ****" && \
   cd /ansible && \
-  ansible-playbook -i inventory site.yml $EXTRA_VARS
+  ansible-playbook -i inventory site.yml ${EXTRA_VARS}
 
 # runtime stage
 FROM alpine:latest