[7.x][ML] Increase open job wait time in MlDistributedFailureIT (#54792) (#54798)

It seems the 20 seconds timeout is occasionally not enough.
We still get sporadic failures where the logs reveal the job
wasn't opened within 20 seconds. I'm increasing the wait time
to 30 seconds.

Closes #54448

Backport of #54792

x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/integration/MlDistributedFailureIT.java

@@ -437,7 +437,7 @@ public class MlDistributedFailureIT extends BaseMlIntegTestCase {
             GetJobsStatsAction.Response statsResponse =
                     client().execute(GetJobsStatsAction.INSTANCE, new GetJobsStatsAction.Request(job.getId())).actionGet();
             assertEquals(JobState.OPENED, statsResponse.getResponse().results().get(0).getState());
-        }, 20, TimeUnit.SECONDS);
+        }, 30, TimeUnit.SECONDS);
 
         setMlIndicesDelayedNodeLeftTimeoutToZero();