[TEST] Increase ML distributed test job open timeout (#50998)

There have been occasional failures, presumably due to
too many tests running in parallel, caused by jobs taking
around 15 seconds to open.  (You can see the job open
successfully during the cleanup phase shortly after the
failure of the test in these cases.)  This change increases
the wait time from 10 seconds to 20 seconds to reduce the
risk of this happening.

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

@@ -416,7 +416,7 @@ 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);
 
         StartDatafeedAction.Request startDatafeedRequest = new StartDatafeedAction.Request(config.getId(), 0L);
         client().execute(StartDatafeedAction.INSTANCE, startDatafeedRequest).get();