update missing translation string (#16559)

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

i18n/en.json

@@ -3220,7 +3220,7 @@
   },
   {
     "id": "api.user.get_authorization_code.endpoint.app_error",
-    "translation": "Failed to get authorization code."
+    "translation": "Error retreiving endpoint from Discovery Document."
   },
   {
     "id": "api.user.get_uploads_for_user.forbidden.app_error",