Mute TaskManagerTests#testTrackingChannelTask

It fails sometimes. Tracked by #56746.

server/src/test/java/org/elasticsearch/tasks/TaskManagerTests.java

@@ -76,6 +76,7 @@ public class TaskManagerTests extends ESTestCase {
         assertEquals(600000L, total);
     }
 
+    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/56746")
     public void testTrackingChannelTask() throws Exception {
         final TaskManager taskManager = new TaskManager(Settings.EMPTY, threadPool, Set.of());
         Set<CancellableTask> cancelledTasks = ConcurrentCollections.newConcurrentSet();