changed magic method __wakeup in AdminPanel to public because wp require this

Author: grzegorz-jamroz

src/CustomAdminPage/AdminPage.php

@@ -148,7 +148,7 @@ final private function __clone()
     {
     }
 
-    final private function __wakeup()
+    final public function __wakeup()
     {
     }
 }