fix: content feed manifest language codes on TYPO3 13

SiteLanguage::getTwoLetterIsoCode() is gone; the locale provides the
language code.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/ep_products/Classes/ContentFeed/ManifestBuilder.php

@@ -88,7 +88,7 @@ class ManifestBuilder
         $languages = [];
 
         foreach ($site->getLanguages() as $language) {
-            $languages[] = $language->getTwoLetterIsoCode();
+            $languages[] = $language->getLocale()->getLanguageCode();
         }
 
         $title = trim((string) ($site->getConfiguration()['websiteTitle'] ?? ''));
@@ -121,7 +121,7 @@ class ManifestBuilder
 
             foreach ($site->getLanguages() as $language) {
                 if (in_array($language->getLanguageId(), $feedLanguages, true)) {
-                    $languageIds[$language->getLanguageId()] = $language->getTwoLetterIsoCode();
+                    $languageIds[$language->getLanguageId()] = $language->getLocale()->getLanguageCode();
                 }
             }