don't debug-print an Any

[RalfJung]

A supervisor panic would look something like this

Supervisor process panicked!
Any { .. }

Try running again without using the native-lib tracer.

Printing an Any isn't very useful, so let's skip that part.

[rustbot]

Thank you for contributing to Miri!
Please remember to not force-push to the PR branch except when you need to rebase due to a conflict or when the reviewer asks you for it.