diff.carp: reference lifetime error in `Map.put` inside inner loop

[hellerve]

Running carp -x tests/diff.carp fails to compile:

The reference '(ref iold)' (depending on the variable '(Int.inc (if (/=__int iold 0) (do (Map.get__int_int (ref overlap) (ref (Int.dec iold)))) (do iold)))') isn't alive

The offending site is the Map.put _overlap &iold &(Int.inc ...) inside the inner for [i 0 (Array.length ol)] loop: the value expression (Int.inc (if (/= iold 0) (Map.get &overlap &(Int.dec iold)) iold)) depends on a reference whose source can be moved away by the Map.put's ownership.

CI has continue-on-error: true on the Run tests step, so this has been silently broken.