fix test

Author: ywangd

x-pack/plugin/transform/src/test/java/org/elasticsearch/xpack/transform/action/TransportSetTransformUpgradeModeActionTests.java

@@ -193,7 +193,7 @@ private ClusterState stateWithTransformTask() {
 
     public void testDisableUpgradeMode() throws InterruptedException {
         doAnswer(ans -> {
-            ActionListener<Boolean> listener = ans.getArgument(2);
+            ActionListener<Boolean> listener = ans.getArgument(3);
             listener.onResponse(true);
             return null;
         }).when(persistentTasksService).waitForPersistentTasksCondition(any(), any(), any(), any());