Nonexistent test sets are too happy to generate an empty xml
Looking into the setup stage, kpet is called with --sets trace
which according to kpet-db, doesn't exist: https://gitlab.com/cki-project/kpet-db/-/blob/main/index.yaml#L442
kpet happily generated an empty xml which the test run understandably borked on. Instead, kpet should loudly complain about any invalid test sets it gets.