Fix E-notice about visibility of __wakeup magic methods not being public
As per the PHP documentation
"All magic methods, with the exception of __construct(), __destruct(), and __clone(), must be declared as public, otherwise an E_WARNING is emitted. Prior to PHP 8.0.0, no diagnostic was emitted for the magic methods __sleep(), __wakeup(), __serialize(), __unserialize(), and __set_state()." https://www.php.net/manual/en/language.oop5.magic.php