fix blocking issue when cell contains ipywidget

Author: huajie.liu

nbclient/client.py

@@ -772,6 +772,8 @@ async def _async_poll_for_reply(
             deadline = monotonic() + timeout
             new_timeout = float(timeout)
         else:
+            # if we set new_timeout None value , and pass to the function of shell_channel.get_msg, will sometimes
+            # blocking so need pass a timeout value, and reset the value when timeout value exhausted
             deadline = monotonic() + 5
             new_timeout = float(5)
         error_on_timeout_execute_reply = None