Fix an error when updating SPA configuration on Cloud module admin page

Problem/Motivation

• When updating any of the SPA settings on the /admin/config/services/cloud/settings page, the user submitted settings are ignored if the Use React single page application (SPA) is checked.
• The following code in the CloudAdminSettings::submitForm() prevents the user from updating those settings.
  

      if ($use_spa && !$use_spa_by_config) {
        $this->enableSpaApp(
          $form_state->getValue('cloud_spa_key_directory'),
          $form_state->getValue('cloud_spa_callback_url')
        );
      }
      elseif (!$use_spa) {
        $this->disableSpaApp();
      }