crypto/internal/cryptotest: use linux-amd64_avx512 builder for SHA-NI

crypto/internal/cryptotest: use linux-amd64_avx512 builder for SHA-NI

Updates #74772
Fixes #69592

Change-Id: I6a6a69647ab1785ed953f3ed2dfa04cd55576f2b
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64_avx512
Reviewed-on: https://go-review.googlesource.com/c/go/+/701315
Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>
Reviewed-by: Mark Freeman <markfreeman@google.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>