crypto/internal/cryptotest: skip TestAllocations on s390x

crypto/internal/cryptotest: skip TestAllocations on s390x

TestXAESAllocations fails like #70448, and crypto/rand's fails in FIPS
mode. We can't keep chasing these without even a LUCI builder.

Updates #67307

Change-Id: I5d0edddf470180a321dec55cabfb018db62eb940
Reviewed-on: https://go-review.googlesource.com/c/go/+/636055
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>