Handle actors with no ID key

[simonw]

This came up running tests on another project with this as a dependency:

  File ".../site-packages/datasette_acl/__init__.py", line 198, in update_dynamic_groups
    if (not skip_cache) and one_second_cache.get(actor["id"]):
                                                 ~~~~~^^^^^^

[simonw]

Actually this happened for an actor that looked like this:

(Pdb) actor
{'_datasette_enrichments': True}

That's a trick that https://github.com/datasette/datasette-enrichments uses.