[MINOR] update HiveExternalCatalogVersionsSuite to test 2.4.0

## What changes were proposed in this pull request?

Since Spark 2.4.0 is released, we should test it in HiveExternalCatalogVersionsSuite

## How was this patch tested?

N/A

Closes apache#22984 from cloud-fan/minor.

Authored-by: Wenchen Fan <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>
(cherry picked from commit 973f7c0)
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: cloud-fan

sql/hive/src/test/scala/org/apache/spark/sql/hive/HiveExternalCatalogVersionsSuite.scala

@@ -203,7 +203,7 @@ class HiveExternalCatalogVersionsSuite extends SparkSubmitTestUtils {
 
 object PROCESS_TABLES extends QueryTest with SQLTestUtils {
   // Tests the latest version of every release line.
-  val testingVersions = Seq("2.1.3", "2.2.2", "2.3.2")
+  val testingVersions = Seq("2.2.2", "2.3.2", "2.4.0")
 
   protected var spark: SparkSession = _