Increase TTL in dead lettering tests

Those fail sometimes on CI, increasing TTL can help on slow-ish
environment.

(cherry picked from commit 44c3ca2)

Author: acogoluegnes

src/test/java/com/rabbitmq/client/test/functional/DeadLetterExchange.java

@@ -34,7 +34,7 @@ public class DeadLetterExchange extends BrokerTestCase {
     public static final String DLQ = "queue.dlq";
     private static final String DLQ2 = "queue.dlq2";
     public static final int MSG_COUNT = 10;
-    private static final int TTL = 1000;
+    private static final int TTL = 2000;
 
     @Override
     protected void createResources() throws IOException {