Fix ClusterInfoServiceIT#testMaxQueueLatenciesInClusterInfo

Closes: #134500

Author: nicktindall

muted-tests.yml

@@ -444,9 +444,6 @@ tests:
 - class: org.elasticsearch.action.admin.cluster.state.TransportClusterStateActionTests
   method: testGetClusterStateWithDefaultProjectOnly
   issue: https://github.com/elastic/elasticsearch/issues/134450
-- class: org.elasticsearch.cluster.ClusterInfoServiceIT
-  method: testMaxQueueLatenciesInClusterInfo
-  issue: https://github.com/elastic/elasticsearch/issues/134500
 - class: org.elasticsearch.xpack.esql.expression.function.scalar.score.DecayTests
   method: "testEvaluateBlockWithNulls {TestCase=<date_nanos>, <date_nanos>, <time_duration>, <_source> #11}"
   issue: https://github.com/elastic/elasticsearch/issues/134509

server/src/internalClusterTest/java/org/elasticsearch/cluster/ClusterInfoServiceIT.java

@@ -514,6 +514,8 @@ public void testMaxQueueLatenciesInClusterInfo() throws Exception {
                 threadsToJoin[i].join();
             }
             Arrays.stream(threadsToJoin).forEach(thread -> assertFalse(thread.isAlive()));
+            // Wait for the write executor to go idle
+            assertBusy(() -> assertThat(trackingWriteExecutor.getActiveCount(), equalTo(0)));
 
             assertThat(
                 "Unexpectedly found a task queued for the write thread pool. Write thread pool dump: " + trackingWriteExecutor,