Fix what reported by phpcs

Updated Symfony\Contracts\EventDispatcher\Event to Drupal\Component\EventDispatcher\Event for Drupal 9/10 compatibility and Symfony 5 forward compatibility.

Closes #3203024

src/Events/DefaultParagraphsAddEvent.php

@@ -2,8 +2,8 @@
 
 namespace Drupal\default_paragraphs\Events;
 
+use Drupal\Component\EventDispatcher\Event;
 use Drupal\paragraphs\ParagraphInterface;
-use Symfony\Component\EventDispatcher\Event;
 
 /**
  * Represents Paragraph Entity adding as default.