[SPARK-31248][CORE][TEST] Fix flaky ExecutorAllocationManagerSuite.in…

…terleaving add and remove

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

This PR (SPARK-31248) uses `ManualClock` to disable `ExecutorAllocationManager.schedule()`  in order to avoid unexpected update of target executors.

### Why are the changes needed?

`ExecutorAllocationManager` will call `schedule` periodically, which may update target executors before we checking https://github.com/apache/spark/blob/496f6ac86001d284cbfb7488a63dd3a168919c0f/core/src/test/scala/org/apache/spark/ExecutorAllocationManagerSuite.scala#L864

And fail the check:

```
sbt.ForkMain$ForkError: org.scalatest.exceptions.TestFailedException: 12 did not equal 8
	at org.scalatest.Assertions.newAssertionFailedException(Assertions.scala:530)
	at org.scalatest.Assertions.newAssertionFailedException$(Assertions.scala:529)
	at org.scalatest.FunSuite.newAssertionFailedException(FunSuite.scala:1560)
	at org.scalatest.Assertions$AssertionsHelper.macroAssert(Assertions.scala:503)
	at org.apache.spark.ExecutorAllocationManagerSuite.$anonfun$new$51(ExecutorAllocationManagerSuite.scala:864)
	at org.scalatest.OutcomeOf.outcomeOf(OutcomeOf.scala:85)
	at org.scalatest.OutcomeOf.outcomeOf$(OutcomeOf.scala:83)
	at org.scalatest.OutcomeOf$.outcomeOf(OutcomeOf.scala:104)
	at org.scalatest.Transformer.apply(Transformer.scala:22)
	at org.scalatest.Transformer.apply(Transformer.scala:20)
	at org.scalatest.FunSuiteLike$$anon$1.apply(FunSuiteLike.scala:186)
	at org.apache.spark.SparkFunSuite.withFixture(SparkFunSuite.scala:151)
	at org.scalatest.FunSuiteLike.invokeWithFixture$1(FunSuiteLike.scala:184)
```

### Does this PR introduce any user-facing change?

No.

### How was this patch tested?

Update test.

Closes apache#28084 from Ngone51/spark_31248.

Authored-by: yi.wu <yi.wu@databricks.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

core/src/main/scala/org/apache/spark/ExecutorAllocationManager.scala

@@ -437,7 +437,7 @@ private[spark] class ExecutorAllocationManager(
           } else {
             logDebug(s"Lowering target number of executors to" +
               s" ${numExecutorsTargetPerResourceProfileId(rpId)} (previously " +
-              s"$targetNum.oldNumExecutorsTarget for resource profile id: ${rpId}) " +
+              s"${targetNum.oldNumExecutorsTarget} for resource profile id: ${rpId}) " +
               "because not all requested executors " +
               "are actually needed")
           }

core/src/test/scala/org/apache/spark/ExecutorAllocationManagerSuite.scala

@@ -841,7 +841,10 @@ class ExecutorAllocationManagerSuite extends SparkFunSuite {
   }
 
   test ("interleaving add and remove") {
-    val manager = createManager(createConf(5, 12, 5))
+    // use ManualClock to disable ExecutorAllocationManager.schedule()
+    // in order to avoid unexpected update of target executors
+    val clock = new ManualClock()
+    val manager = createManager(createConf(5, 12, 5), clock)
     post(SparkListenerStageSubmitted(createStageInfo(0, 1000)))
 
     val updatesNeeded =