Fix ConsumerAcknowledgment,toString()

Use `ListenerUtils` for record.

Author: garyrussell

spring-kafka/src/main/java/org/springframework/kafka/listener/KafkaMessageListenerContainer.java

@@ -2864,7 +2864,7 @@ public void nack(long sleep) {
 
 			@Override
 			public String toString() {
-				return "Acknowledgment for " + this.record;
+				return "Acknowledgment for " + ListenerUtils.recordToString(this.record);
 			}
 
 		}