Fix new translation is missing the relation id for saving

Author: Tofandel

src/Translatable/Translatable.php

@@ -181,6 +181,7 @@ public function getNewTranslation(string $locale): Model
         /** @var Model $translation */
         $translation = new $modelName();
         $translation->setAttribute($this->getLocaleKey(), $locale);
+        $translation->setAttribute($this->translations()->getForeignKeyName(), $this->getKey());
         $this->translations->add($translation);
 
         return $translation;