fix: make closeAsync don't interrupt running thread (#1446)

Author: mutianf

gax/src/main/java/com/google/api/gax/batching/BatcherImpl.java

@@ -328,7 +328,7 @@ public ApiFuture<Void> closeAsync() {
     }
 
     // Clean up accounting
-    scheduledFuture.cancel(true);
+    scheduledFuture.cancel(false);
     currentBatcherReference.closed = true;
     currentBatcherReference.clear();