windows: downgrade messages on coro exceptions to debug

Author: hartytp

qasync/_windows.py

@@ -42,7 +42,7 @@ def _process_events(self, events):
                 self._logger.debug('Invoking event callback {}'.format(callback))
                 value = callback(transferred, key, ov)
             except OSError:
-                self._logger.warning('Event callback failed', exc_info=sys.exc_info())
+                self._logger.debug('Event callback failed', exc_info=sys.exc_info())
             else:
                 if not f.cancelled():
                     f.set_result(value)