[SPARK-29139][CORE][TESTS] Increase timeout to wait for executor(s) to be up in SparkContextSuite

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

This patch proposes to increase timeout to wait for executor(s) to be up in SparkContextSuite, as we observed these tests failed due to wait timeout.

### Why are the changes needed?

There's some case that CI build is extremely slow which requires 3x or more time to pass the test.
(https://issues.apache.org/jira/browse/SPARK-29139?focusedCommentId=16934034&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-16934034)

Allocating higher timeout wouldn't bring additional latency, as the code checks the condition with sleeping 10 ms per loop iteration.

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

No

### How was this patch tested?

N/A, as the case is not likely to be occurred frequently.

Closes #25864 from HeartSaVioR/SPARK-29139.

Authored-by: Jungtaek Lim (HeartSaVioR) <kabhwan@gmail.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>

Author: HeartSaVioR

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

@@ -761,7 +761,7 @@ class SparkContextSuite extends SparkFunSuite with LocalSparkContext with Eventu
       sc = new SparkContext(conf)
 
       // Ensure all executors has started
-      TestUtils.waitUntilExecutorsUp(sc, 1, 10000)
+      TestUtils.waitUntilExecutorsUp(sc, 1, 60000)
       assert(sc.resources.size === 1)
       assert(sc.resources.get(GPU).get.addresses === Array("5", "6"))
       assert(sc.resources.get(GPU).get.name === "gpu")
@@ -790,7 +790,7 @@ class SparkContextSuite extends SparkFunSuite with LocalSparkContext with Eventu
       sc = new SparkContext(conf)
 
       // Ensure all executors has started
-      TestUtils.waitUntilExecutorsUp(sc, 1, 10000)
+      TestUtils.waitUntilExecutorsUp(sc, 1, 60000)
       // driver gpu resources file should take precedence over the script
       assert(sc.resources.size === 1)
       assert(sc.resources.get(GPU).get.addresses === Array("0", "1", "8"))