fix: reset keep_alive_task to None

Author: Lash-L

roborock/devices/local_channel.py

@@ -204,6 +204,7 @@ def close(self) -> None:
         """Disconnect from the device."""
         if self._keep_alive_task:
             self._keep_alive_task.cancel()
+            self._keep_alive_task = None
         if self._transport:
             self._transport.close()
         else:
@@ -216,6 +217,7 @@ def _connection_lost(self, exc: Exception | None) -> None:
         _LOGGER.warning("Connection lost to %s", self._host, exc_info=exc)
         if self._keep_alive_task:
             self._keep_alive_task.cancel()
+            self._keep_alive_task = None
         self._transport = None
         self._is_connected = False