Fix test for SK 2.2.4

Override deserializer getters in test consumer factory because the
defaults incorrectly throw an `UnsupportedOperationException`.

See https://github.com/spring-projects/spring-kafka/pull/963

spring-cloud-stream-binder-kafka/src/test/java/org/springframework/cloud/stream/binder/kafka/KafkaBinderUnitTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2018 the original author or authors.
+ * Copyright 2017-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,6 +35,7 @@ import org.apache.kafka.clients.consumer.ConsumerRecords;
 import org.apache.kafka.clients.producer.ProducerConfig;
 import org.apache.kafka.common.PartitionInfo;
 import org.apache.kafka.common.TopicPartition;
+import org.apache.kafka.common.serialization.Deserializer;
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
 
@@ -263,6 +264,16 @@ public class KafkaBinderUnitTests {
 						return props;
 					}
 
+					@Override
+					public Deserializer<byte[]> getKeyDeserializer() {
+						return null;
+					}
+
+					@Override
+					public Deserializer<byte[]> getValueDeserializer() {
+						return null;
+					}
+
 				};
 			}