[hotfix] [tests] Reduce visibility of helper class methods

There is no need to make the helper methods public. No other class
should even use this inner test helper invokable.

flink-runtime/src/test/java/org/apache/flink/runtime/jobmanager/JobManagerHARecoveryTest.java

@@ -622,16 +622,16 @@ public void notifyCheckpointComplete(long checkpointId) {
 			}
 		}
 
-		public static void initializeStaticHelpers(int numSubtasks) {
+		static void initializeStaticHelpers(int numSubtasks) {
 			completedCheckpointsLatch = new CountDownLatch(numSubtasks);
 			recoveredStates = new long[numSubtasks];
 		}
 
-		public static void awaitCompletedCheckpoints() throws InterruptedException {
+		static void awaitCompletedCheckpoints() throws InterruptedException {
 			completedCheckpointsLatch.await();
 		}
 
-		public static long[] getRecoveredStates() {
+		static long[] getRecoveredStates() {
 			return recoveredStates;
 		}