crypto/internal/fips/aes/gcm: skip TestAllocations on PPC64

crypto/internal/fips/aes/gcm: skip TestAllocations on PPC64

TestAllocations is failing on PPC64 causing all PPC64 CI to fail.

Skip the test until it can be debugged.

For #70448

Change-Id: Ic18e402f4af5939a90eba2e1f2b182699013ed55
Reviewed-on: https://go-review.googlesource.com/c/go/+/629697
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>