ci: Prune dangling images on RESTART_CI_DOCKER_BEFORE_RUN

Author: MarcoFalke

ci/test/04_install.sh

@@ -43,6 +43,8 @@ if [ -z "$DANGER_RUN_CI_ON_HOST" ]; then
   if [ -n "${RESTART_CI_DOCKER_BEFORE_RUN}" ] ; then
     echo "Restart docker before run to stop and clear all containers started with --rm"
     systemctl restart docker
+    echo "Prune all dangling images"
+    docker image prune --force
   fi
 
   # shellcheck disable=SC2086