Prevent using deprecated method

[ayacoo]

TYPO3 v13

Call to undefined method TYPO3\CMS\Core\Site\Entity\SiteLanguage::getTwoLetterIsoCode()
in /var/www/html/vendor/wapplersystems/videos/Classes/Resource/Rendering/VideoTagRenderer.php line 167

"SiteLanguage->getTwoLetterIsoCode() will be removed in TYPO3 v13.0. Use SiteLanguage->getLocale()->getLanguageCode() instead."