fix a mistake

core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala

@@ -123,7 +123,7 @@ private[spark] class TaskSetManager(
   // state until all tasks have finished running; we keep TaskSetManagers that are in the zombie
   // state in order to continue to track and account for the running tasks.
   // TODO: We should kill any running task attempts when the task set manager becomes a zombie.
-  @transient private[scheduler] var isZombie = false
+  @volatile private[scheduler] var isZombie = false
 
   // Whether the taskSet run tasks from a barrier stage. Spark must launch all the tasks at the
   // same time for a barrier stage.