Fix invalid interface mention in security.rst

SerializableInterface doesn't exist, I assume it was meant to be https://www.php.net/manual/en/class.serializable.php, the motivation behind this change is described here https://stackoverflow.com/questions/42074225/symfony-userinterface-is-serializing-the-entire-massive-user-entity/71816482#71816482

Author: ttibensky

security.rst

@@ -2503,9 +2503,9 @@ However, in some cases, this process can cause unexpected authentication problem
 If you're having problems authenticating, it could be that you *are* authenticating
 successfully, but you immediately lose authentication after the first redirect.
 
-In that case, review the serialization logic (e.g. ``SerializableInterface``) on
+In that case, review the serialization logic (e.g. ``\Serializable`` interface) on
 you user class (if you have any) to make sure that all the fields necessary are
-serialized.
+serialized and also exclude all the fields not necessary to be serialized (relations).
 
 Comparing Users Manually with EquatableInterface
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~