shake error when switching between stack-build and pier-built pier

[simonmichael]

Perhaps not a bug, just FYI: I built a pier1 binary with stack, and a pier2 binary with pier1. They chose different shake versions, so whenever I switch from one to the other I get one-time warnings like:

Error when reading Shake database _pier/.shake.database
  Witness type has disappeared, StepKey {28f7ba3f6dfe3236}
  CallStack (from HasCallStack):
    error, called at _pier/artifact/sfxt5h5guBiphjkbCgsu5T6T8jBOJ1PujYwYHuy.kSU/package/raw/shake-0.16/src/Development/Shake/Internal/Core/Storage.hs:190:40 in shake-0.16:Development.Shake.Internal.Core.Storage
All files will be rebuilt

�]0;Starting...��]0;1s (85%)��]0;1s (85%)��]0;Finished�Build completed in 0:13m

Error when reading Shake database _pier/.shake.database
  Witness type has disappeared, StepKey {3046876bdc36b7ab}
  CallStack (from HasCallStack):
    error, called at src/Development/Shake/Internal/Core/Storage.hs:191:40 in shake-0.16.3-8Fw9R0rUGu8HU9lcExNHef:Development.Shake.Internal.Core.Storage
All files will be rebuilt

�]0;Starting...��]0;Finished�Build completed in 0:03m