404 error on click on held message in list because the trailing slash is missing

When you look at the list of held messages, and click on one message, then you expect to see the popup with the details of the held message. But I get on the webbrowser console a 404 error, because it is trying to get the message without the trailing slash: /mailman3/api/list/mylist.example.org/held_message/1

see https://gitlab.com/mailman/postorius/-/blob/master/src/postorius/static/postorius/js/held_messages.js?ref_type=heads#L9 no trailing slash is added

But in https://gitlab.com/mailman/postorius/-/blob/master/src/postorius/urls.py?ref_type=heads#L237 a trailing slash is expected.

I wonder if something is wrong with my setup, or is it a bug?