Fix PHP 7.4 deprecations

inc/lib/Twig/Template.php

@@ -579,7 +579,7 @@ abstract class Twig_Template implements Twig_TemplateInterface
 
         // object property
         if (self::METHOD_CALL !== $type && !$object instanceof self) { // Twig_Template does not have public properties, and we don't want to allow access to internal ones
-            if (isset($object->$item) || array_key_exists((string) $item, $object)) {
+            if (isset($object->$item) || property_exists($object, (string) $item)) {
                 if ($isDefinedTest) {
                     return true;
                 }