Add public keyword to methods

[MAILPOET-2413]

tests/integration/Config/HooksTest.php

@@ -6,7 +6,7 @@ use MailPoet\Config\Hooks;
 use MailPoet\DI\ContainerWrapper;
 
 class HooksTest extends \MailPoetTest {
-  function testItHooksSchedulerToMultiplePostTypes() {
+  public function testItHooksSchedulerToMultiplePostTypes() {
     $hooks = ContainerWrapper::getInstance()->get(Hooks::class);
     $hooks->setupPostNotifications();
     expect(has_filter('transition_post_status'))->notEmpty();