fix: also loaad dark-mode switch defer'Ed to make it load correctly

(async fails on WebKIt)

tpl/bootstrap5.php

@@ -42,7 +42,7 @@ endif;
 		<?php $this->_scriptTag('js/base-x-4.0.0.js', ''); ?>
 		<?php $this->_scriptTag('js/rawinflate-0.3.js', ''); ?>
 		<?php $this->_scriptTag('js/bootstrap-5.3.3.js', 'async'); ?>
-		<?php $this->_scriptTag('js/dark-mode-switch.js', 'async'); ?>
+		<?php $this->_scriptTag('js/dark-mode-switch.js', 'defer'); ?>
 <?php
 if ($SYNTAXHIGHLIGHTING) :
 ?>