#3221 introduced additional pointer validity checks when performing pointer-to-reference casts to aid with modular verification.

This led to one harness run on the CI inside s2n-quic timing out, so the checks were introduced behind an unstable flag. The reason for the timeout was that a check was inserted inside a nested loop, which blew up verification time.

One of the pathways for stabilizing the checks is excluding the harness from the CI.