mqtt tests: connect to local broker when running in CI to make the tests more reliable

examples/protocols/mqtt/ws/main/app_main.c

@@ -118,7 +118,7 @@ static void wifi_init(void)
 static void mqtt_app_start(void)
 {
     const esp_mqtt_client_config_t mqtt_cfg = {
-        .uri = "ws://iot.eclipse.org:80/ws",
+        .uri = CONFIG_BROKER_URI,
         .event_handle = mqtt_event_handler,
         // .user_context = (void *)your_context
     };