use REDIS_PORT to replace 6379 in celery config (#16182)

api/.env.example

 # Refresh token expiration time in days
 REFRESH_TOKEN_EXPIRE_DAYS=30
 
-# celery configuration
-CELERY_BROKER_URL=redis://:difyai123456@localhost:6379/1
-
 # redis configuration
 REDIS_HOST=localhost
 REDIS_PORT=6379
 REDIS_CLUSTERS=
 REDIS_CLUSTERS_PASSWORD=
 
+# celery configuration
+CELERY_BROKER_URL=redis://:difyai123456@localhost:${REDIS_PORT}/1
+
 # PostgreSQL database configuration
 DB_USERNAME=postgres
 DB_PASSWORD=difyai123456