test(batch): acks data synchronously

Author: bevzzz

src/test/java/io/weaviate/client6/v1/api/collections/batch/BatchContextTest.java

@@ -502,7 +502,7 @@ public void test_startAfterClose() throws Exception {
    */
   private List<String> recvDataAndAck() throws InterruptedException {
     List<String> received = recvData();
-    out.emitEventAsync(new Event.Acks(received));
+    out.emitEvent(new Event.Acks(received));
     return received;
   }