[SPARK-29263][SCHEDULER][FOLLOWUP][TEST] Update FakeTask.createTaskSet() method

### What changes were proposed in this pull request?

Update `FakeTask.createTaskSet()` method to make the generated TaskSet makes use of the `priority` param.

### How was this patch tested?

All the places referring to this method pass `priority = 0`, but we still need to fix this to avoid future test failure.

Closes apache#26030 from jiangxb1987/SPARK-292630-FOLLOWUP.

Authored-by: Xingbo Jiang <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: jiangxb1987

core/src/test/scala/org/apache/spark/scheduler/FakeTask.scala

@@ -65,7 +65,7 @@ object FakeTask {
     val tasks = Array.tabulate[Task[_]](numTasks) { i =>
       new FakeTask(stageId, i, if (prefLocs.size != 0) prefLocs(i) else Nil)
     }
-    new TaskSet(tasks, stageId, stageAttemptId, priority = 0, null)
+    new TaskSet(tasks, stageId, stageAttemptId, priority = priority, null)
   }
 
   def createShuffleMapTaskSet(