fix: prevent spurious output from possible ``docker pull`` to polute stdout

bin/compose-core

@@ -434,7 +434,7 @@ cached_cmd_on_base_image() {
     fi
     base_image=$(service_base_docker_image "$service") || return 1
     if ! docker_has_image "$base_image"; then
-        docker pull "$base_image"
+        docker pull "$base_image" 1>&2
     fi
     result=$(cached_cmd_on_image "$base_image" "$@") || return 1
     echo "$result" | tee "$cache_file"