feat: explicitly set USER root

- paketo doesn't have a default user root

Authored-by: Preethi Varambally <[email protected]>

dockerfiles/ubuntu/Dockerfile

@@ -14,6 +14,7 @@ RUN set -e; mkdir /tests; for pkg in $(go list ./...); do \
 	done
 
 FROM ${base_image} AS resource
+USER root
 RUN apt update && apt upgrade -y -o Dpkg::Options::="--force-confdef"
 RUN apt update \
       && DEBIAN_FRONTEND=noninteractive \