fix celery config (#22566)

Signed-off-by: kenwoodjw <blackxin55+@gmail.com>

docker/docker-compose.yaml

@@ -79,6 +79,7 @@ x-shared-env: &shared-api-worker-env
   REDIS_CLUSTERS: ${REDIS_CLUSTERS:-}
   REDIS_CLUSTERS_PASSWORD: ${REDIS_CLUSTERS_PASSWORD:-}
   CELERY_BROKER_URL: ${CELERY_BROKER_URL:-redis://:difyai123456@redis:6379/1}
+  CELERY_BACKEND: ${CELERY_BACKEND:-redis}
   BROKER_USE_SSL: ${BROKER_USE_SSL:-false}
   CELERY_USE_SENTINEL: ${CELERY_USE_SENTINEL:-false}
   CELERY_SENTINEL_MASTER_NAME: ${CELERY_SENTINEL_MASTER_NAME:-}