message: fix build break from using `await` instead of `co_await`
diff: @@ -211,7 +211,7 @@ namespace winrt::TerminalApp::implementation
  _root.Children().Append(dialog);
  // Display the dialog.
  - Controls::ContentDialogResult result = await dialog.ShowAsync(Controls::ContentDialogPlacement::Popup);
  + Controls::ContentDialogResult result = co_await dialog.ShowAsync(Controls::ContentDialogPlacement::Popup);
  // After the dialog is dismissed, the dialog lock (held by `lock`) will
  // be released so another can be shown.
  