Containerfile: refactor Label definition to fix LegacyKeyValueFormat warning

Author: stendler

Diff for: Containerfile

@@ -1,6 +1,6 @@
 FROM quay.io/podman/stable
 
-LABEL RUN podman run --rm --volume \$XDG_RUNTIME_DIR/podman:/run/podman:z --env NTFY_USER=\$USER --env NTFY_HOSTNAME=\$HOST -security-opt label=disable IMAGE
+LABEL RUN="podman run --rm --volume \$XDG_RUNTIME_DIR/podman:/run/podman:z --env NTFY_USER=\$USER --env NTFY_HOSTNAME=\$HOST -security-opt label=disable IMAGE"
 
 ENTRYPOINT [ "/containers-check-update.sh" ]