Fix injection glitch added in #91 (#92)

#91 was too eager in skipping the injections of translatable proxies: We
only need to avoid duplicate entries in the list of entities with
translatables, but we must not skip injection of the proxies after
`flush()` operations.

Author: mpdude

src/Doctrine/PolyglotListener.php

@@ -76,10 +76,6 @@ public function prePersist(LifecycleEventArgs $event): void
 
     private function injectPersistentTranslatables(EntityManager $entityManager, object $object): void
     {
-        if (isset($this->entitiesWithTranslatables[$object])) {
-            return;
-        }
-
         $hasTranslatables = false;
 
         foreach ($this->getTranslationMetadatas($object, $entityManager) as $tm) {