fix(MQTT Node): Close connection if connection attempt fails (#10873)

packages/nodes-base/nodes/MQTT/GenericFunctions.ts

@@ -1,5 +1,6 @@
 import { connect, type IClientOptions, type MqttClient } from 'mqtt';
 import { ApplicationError, randomString } from 'n8n-workflow';
+
 import { formatPrivateKey } from '@utils/utilities';
 
 interface BaseMqttCredential {
@@ -62,6 +63,10 @@ export const createClient = async (credentials: MqttCredential): Promise<MqttCli
 		const onError = (error: Error) => {
 			client.removeListener('connect', onConnect);
 			client.removeListener('error', onError);
+			// mqtt client has an automatic reconnect mechanism that will
+			// keep trying to reconnect until it succeeds unless we
+			// explicitly close the client
+			client.end();
 			reject(new ApplicationError(error.message));
 		};