https://github.com/phpbb/phpbb/blob/develop-ascraeus/phpBB/includes/mcp/mcp_queue.php#L746-L753

As !$post_data['topic_posts_approved'] means unapproved topic, it seems that in this case 'notification.type.approve_topic' should be added instaed of 'notification.type.approve_post' and vise versa.

Now, when post is getting approved, user is getting topic approval notification, and vise versa.