message: Monitoring: Fix JS warning on silence save form
  `setInProgress` was being called after navigating to a new page, which
  caused a warning about trying to set component state after the component
  was unmounted. The solution is to simply not call `setInProgress` in
  this case since the component is unmounting anyway.
diff: @@ -1389,8 +1389,10 @@ const SilenceForm_: React.FC<SilenceFormProps> = ({ defaults, Info, title }) =>
  refreshNotificationPollers();
  history.push(`${SilenceResource.plural}/${encodeURIComponent(_.get(data, 'silenceId'))}`);
  })
  - .catch((err) => setError(_.get(err, 'json.error') || err.message || 'Error saving Silence'))
  - .then(() => setInProgress(false));
  + .catch((err) => {
  + setError(_.get(err, 'json.error') || err.message || 'Error saving Silence');
  + setInProgress(false);
  + });
  };
  return (
  