Fix undefined properties in tests [MAILPOET-2488]

tests/integration/Config/ShortcodesTest.php

@@ -17,6 +17,8 @@ use MailPoet\WP\Functions as WPFunctions;
 use MailPoetVendor\Idiorm\ORM;
 
 class ShortcodesTest extends \MailPoetTest {
+  public $queue;
+  public $newsletter;
   public function _before() {
     parent::_before();
     $newsletter = Newsletter::create();