Work and Display a Custom Post Type as a normal Post

Ok, so I think you could apply the codex example as is:

function search_filter($query) {
  if ( !is_admin() && $query->is_main_query() ) {
    if ($query->is_search) {
      $query->set('post_type', array( 'post', 'actualizacion', 'notificacion' ) );
    }
  }
}
add_action('pre_get_posts','search_filter');

I think you were just missing the !is_admin() check in there…

Hope this helps!