mute TasksClientDocumentationIT testCancelTasks

This commit mutes this test, which has failed twice in CI today.

See #35514

client/rest-high-level/src/test/java/org/elasticsearch/client/documentation/TasksClientDocumentationIT.java

@@ -150,6 +150,7 @@ public class TasksClientDocumentationIT extends ESRestHighLevelClientTestCase {
         }
     }
 
+    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/35514")
     @SuppressWarnings("unused")
     public void testCancelTasks() throws IOException {
         RestHighLevelClient client = highLevelClient();