LinkML Inheritance not working

[sneakers-the-rat]

At the moment we can't do what would be desirable here, which is to have an activitypub.yaml schema inherit and extend activitystreams.yaml, see linked issue below.

I'm going to proceed as if that did work, and fork linkml to make it work, because copying and pasting the whole schema is highly undesirable unless it's a last resort

Blocked by: linkml/linkml#1825