Fix race condition in WanCopyRegionFunctionServiceTest

The test severalExecuteWithDifferentRegionOrSenderAreAllowed was failing
intermittently with 'expected: 5 but was: 3' due to a race condition.

The test creates 5 CompletableFuture tasks using supplyAsync(), but there
was no guarantee that all tasks would start executing before the assertion
checked the execution count.

Solution:
- Added a startLatch CountDownLatch to synchronize task startup
- Each callable now counts down the startLatch when it begins execution
- The test waits for all tasks to start before asserting on the count
- Added throws InterruptedException to the test method signature

This ensures all 5 tasks have called service.execute() and been added to
the executions map before we verify the count, eliminating the race
condition.

Author: sboorlagadda

geode-wan/src/test/java/org/apache/geode/cache/wan/internal/WanCopyRegionFunctionServiceTest.java

@@ -154,11 +154,13 @@ public void cancelAllExecutionsWithRunningExecutionsReturnsCanceledExecutions()
   }
 
   @Test
-  public void severalExecuteWithDifferentRegionOrSenderAreAllowed() {
+  public void severalExecuteWithDifferentRegionOrSenderAreAllowed() throws InterruptedException {
     int executions = 5;
     CountDownLatch latch = new CountDownLatch(executions);
+    CountDownLatch startLatch = new CountDownLatch(executions);
     for (int i = 0; i < executions; i++) {
       Callable<CliFunctionResult> firstExecution = () -> {
+        startLatch.countDown();
         latch.await(GeodeAwaitility.getTimeout().getSeconds(), TimeUnit.SECONDS);
         return null;
       };
@@ -174,6 +176,9 @@ public void severalExecuteWithDifferentRegionOrSenderAreAllowed() {
           });
     }
 
+    // Wait for all tasks to start execution
+    startLatch.await(GeodeAwaitility.getTimeout().getSeconds(), TimeUnit.SECONDS);
+
     // Wait for the functions to start execution
     await().untilAsserted(
         () -> assertThat(service.getNumberOfCurrentExecutions()).isEqualTo(executions));