Fix test exchange declaration

- exchanges are now durable by default and tests fail if the exchange
  already exists on the CI broker (declared by a newer release).

Author: garyrussell

spring-rabbit/src/test/java/org/springframework/amqp/rabbit/annotation/EnableRabbitIntegrationTests.java

@@ -1268,7 +1268,7 @@ interface TxClassLevel {
 
 	@RabbitListener(bindings = @QueueBinding
 			(value = @Queue,
-			exchange = @Exchange(value = "multi.exch.tx", autoDelete = "true"),
+			exchange = @Exchange(value = "multi.exch.tx", autoDelete = "true", durable = "true"),
 			key = "multi.rk.tx"))
 	static class TxClassLevelImpl implements TxClassLevel {