[TEST] Ensure that there is at least one enabled test in elasticsearch-transport-client

Original commit: elastic/x-pack-elasticsearch@092d35dc1c

elasticsearch-transport-client/src/test/java/org/elasticsearch/xpack/client/PreBuiltXPackTransportClientTests.java

@@ -30,4 +30,8 @@ public class PreBuiltXPackTransportClientTests extends RandomizedTest {
         }
     }
 
+    // dummy test so that the tests pass on JDK9 as the only test in this module is disabled on JDK9
+    public void testDummy() {
+
+    }
 }