test/valid-pipelines: trigger.yml does not seem to be valid

[rogpeppe]

As of commit 2fbbfc1

The trigger.yml test does not seem to be valid against the schema.

Specifically the last two steps in that test instance data:

  - trigger: "a-slug"
    soft_fail:
      - exit_status: 1

  - trigger: "a-slug"
    soft_fail:
      - exit_status: "*"

have a value for soft_fail that is not compatible with the soft_fail field for triggerStep as defined in the schema, which only allows boolean-like atoms.

Perhaps it might be worth enabling CI gating on these tests passing?
FWIW I'm not sure whether it's the schema or the instance data that's at fault here.