Add missed translation for file indexing (#17012)

i18n/en.json

@@ -6450,6 +6450,10 @@
     "id": "ent.elasticsearch.not_started.error",
     "translation": "Elasticsearch is not started"
   },
+  {
+    "id": "ent.elasticsearch.post.get_files_batch_for_indexing.error",
+    "translation": "Unable to get the files batch for indexing."
+  },
   {
     "id": "ent.elasticsearch.post.get_posts_batch_for_indexing.error",
     "translation": "Unable to get the posts batch for indexing."