Issue #3300629 by huzooka: Handle different (new) default themes in Drupal core 9.5+

      : $this->container->get('site.path');

    $this->setSetting('file_private_path', $site_path . '/private');

    // Install Bartik and Seven.

    // Install default and default admin themes.

    [$default_theme, $admin_theme] = static::claroAndOliveroAreDefaultThemes()

      ? ['olivero', 'claro']

      : ['bartik', 'seven'];

    $theme_installer = \Drupal::service('theme_installer');

    assert($theme_installer instanceof ThemeInstallerInterface);

    $theme_installer->install(['bartik', 'seven']);

    $theme_installer->install([$default_theme, $admin_theme]);

    $this->config('system.theme')

      ->set('default', 'bartik')

      ->set('admin', 'seven')

      ->set('default', $default_theme)

      ->set('admin', $admin_theme)

      ->save();

    // We have to create at least an anonymous user.

    return version_compare(\Drupal::VERSION, '9.4.0-dev', 'ge');

  }

  /**

   * Whether Claro and Olivero are the default (and default admin) themes.

   *

   * @return bool

   *   Whether Claro and Olivero are the default (and default admin) themes.

   */

  protected static function claroAndOliveroAreDefaultThemes(): bool {

    return version_compare(\Drupal::VERSION, '9.5.0-dev', 'ge');

  }

}