Fixup several tests silently broken by 12e7015a

Fixup several tests silently broken by 12e7015a

A number of tests that we do not run during CI (lack of RDBMS) have run-time
tests concerning backcompat along the lines of:

  $schema->class('Artist')->load_components('PK::Auto...')

The above causes the class' mro to be switched after $schema instantiation
and subsequently triggers the sanitychecker. Instead of ripping these lines
out (without a way to test them) - simply augment the ::Artist based set of
classes to preempt the check failures in the first place.