if i put that url in a browser i get the same errors, so the problem is in the website.
you cant fix that yourself, it needs to be fixed at the darksky website.
you could create your own html page that contains the widget and the element “customize-script-container”
and use the url from that html page in your widget.
if a make a simple html code, it works. (outside HA, Apache/2.4.7)
<!DOCTYPE html>
<html>
<body>
<script type=‘text/javascript’ src=‘https://darksky.net/widget/default/42.360082,-71.05888/uk12/en.js?width=100%&height=350&title=Full Forecast&textColor=333333&bgColor=FFFFFF&transparency=false&skyColor=333333&fontFamily=Default&customFont=&units=uk&htColor=333333<Color=C7C7C7&displaySum=yes&displayHeader=yes’></script>
</body>
</html>