Views that allow sorting: sorting by a field without `asc` returns Server Error (500)
E.g. https://debusine.debian.net/work-request/?status=pending&arch=amd64&order=task_name returns HTTP 500. The get_ordering methods (in that case, WorkRequestListView.get_ordering requires asc if order is in the get parameter.
The get_ordering duplicated methods should be re-factored and the fix added there.