DebDiff workflow skips binary comparison for architecture "any" to "all" transitions

Asked/pointed out by @helmutg , I think that there is a problem in a recent change in DebDiffWorkflow (!2663 (merged))

For what I quickly checked: If a binary switches from arch:any to arch:all (new binaries only contain all, original binaries are concrete-only), the workflow schedules no binary debdiff tasks.

I need to write a unit test to be sure that this would be problematic. I don't want to lose track of it.