8274391: Suppress more warnings on non-serializable non-transient instance fields in java.util.concurrent

Reviewed-by: lancea, bpb, alanb, iris

src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java

@@ -2778,6 +2778,7 @@ public class ForkJoinPool extends AbstractExecutorService {
         @SuppressWarnings("serial") // Conditionally serializable
         volatile E result;
         final AtomicInteger count;  // in case all throw
+        @SuppressWarnings("serial")
         final ForkJoinPool pool;    // to check shutdown while collecting
         InvokeAnyRoot(int n, ForkJoinPool p) {
             pool = p;