Ignore zen2 discovery task in waitForPendingTasks (#36381)

Fixes #36380

Author: droberts195

x-pack/plugin/src/test/java/org/elasticsearch/xpack/test/rest/XPackRestIT.java

@@ -9,6 +9,7 @@
 
 import org.apache.http.HttpStatus;
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.action.admin.cluster.bootstrap.GetDiscoveredNodesAction;
 import org.elasticsearch.client.Request;
 import org.elasticsearch.client.Response;
 import org.elasticsearch.common.CheckedFunction;
@@ -255,7 +256,9 @@ public void cleanup() throws Exception {
             // it could be waiting for pending tasks while monitoring is still running).
             ESRestTestCase.waitForPendingTasks(adminClient(), task -> {
                     // Don't check rollup jobs because we clear them in the superclass.
-                    return task.contains(RollupJob.NAME);
+                    return task.contains(RollupJob.NAME)
+                        // Also ignore the zen2 discovery task
+                        || task.contains(GetDiscoveredNodesAction.NAME);
             });
         }
     }