debusine collection list is very slow due to workflow-internal collections

I tried python3 -m debusine.client collection list against the debian/developers workspace on debusine.debian.net, and found it to be so slow that I thought it had hung. In fact it was just iterating through a large number of debusine:workflow-internal collections. Should we exclude those from the list in the same way that we exclude them from the workspace_collections context item in BaseUIView (compare #639 (closed))?