[pulsar-client] print unknown exception stacktrace (#5444)

(cherry picked from commit 0c7319fc)

pulsar-client/src/main/java/org/apache/pulsar/client/impl/ProducerImpl.java

@@ -1306,7 +1306,7 @@ public class ProducerImpl<T> extends ProducerBase<T> implements TimerTask, Conne
                 semaphore.release(batchMessageContainer.getNumMessagesInBatch());
             } catch (Throwable t) {
                 semaphore.release(batchMessageContainer.getNumMessagesInBatch());
-                log.warn("[{}] [{}] error while create opSendMsg by batch message container -- {}", topic, producerName, t);
+                log.warn("[{}] [{}] error while create opSendMsg by batch message container", topic, producerName, t);
             }
         }
     }