fix: do not retire the original image

By removing the image cleanup registration, we avoid cases where we delete gliderlabs/herokuish, which may cause issues for users in airgapped installations (where the image may not be pullable from a registry).

plugins/builder-herokuish/builder-build

@@ -41,7 +41,7 @@ trigger-builder-herokuish-builder-build() {
   fi
 
   "$DOCKER_BIN" container commit "${DOCKER_COMMIT_LABEL_ARGS[@]}" "$CID" "$IMAGE" >/dev/null
-  plugn trigger scheduler-register-retired "$APP" "$CID"
+  DOKKU_SKIP_IMAGE_CLEANUP_REGISTRATION=1 plugn trigger scheduler-register-retired "$APP" "$CID"
 
   [[ -d $DOKKU_APP_CACHE_DIR ]] || mkdir -p "$DOKKU_APP_CACHE_DIR"
   plugn trigger pre-build-buildpack "$APP" "$SOURCECODE_WORK_DIR"