Fix writer stop loop handle

Author: rekby

ydb/_topic_writer/topic_writer_asyncio.py

@@ -537,6 +537,9 @@ async def _send_loop(self, writer: "WriterAsyncIOStream"):
                 m = await self._new_messages.get()  # type: InternalMessage
                 if m.seq_no > last_seq_no:
                     writer.write([m])
+        except asyncio.CancelledError:
+            # the loop task cancelled be parent code, for example for reconnection
+            pass
         except BaseException as e:
             self._stop(e)
             raise