Hook update readonlymode_update_8001 fails.

Hi,

I don't think what your initial patch does what the update hook was meant to be doing.

I think it was intended to convert the 7.x version of the modules config to the 8.x version. It should be something like:

function readonlymode_update_8001() {
  $settings = \Drupal::configFactory()->getEditable("readonlymode.settings");
  if (isset($settings['site_readonly'])) {
    // Config from the 7.x branch needs updating to 8.x structure.
    $new_settings = [
      'enabled' => $settings['site_readonly'],
      'url' => $settings['site_readonly_url'],
      'messages.default' => $settings['site_readonly_message'],
      'forms.additional.edit' => $settings['site_readonly_forms_allowed'],
      'forms.additional.view' => $settings['site_readonly_forms_viewonly'],
    ];
    $settings->setData($new_settings);
    $settings->save();
    return 'Updated readonlymode.settings configuration to 8.x version.';
  }
  return NULL;
}

I haven't tested this as we didn't use the 7.x version.

I think you're right. The changes are completely wrong. Can you update the MR?