Rejects a retry block declared on a step nothing is scheduled for.
A manual step, a wait state, and a terminal step none have a generated
trigger to retry — AshWorkflow.Transformers.AddScheduler only turns an
automatic step into a AshWorkflow.Scheduler.Work, through
AshWorkflow.Entities.Step.manual?/1 and the terminal flag. A retry
block on one of these compiles but does nothing, so it is rejected instead.