runtime: skip testprogcgo tests in race mode on freebsd

runtime: skip testprogcgo tests in race mode on freebsd

These were just enabled by https://go.dev/cl/643897, but freebsd
unfortunately doesn't seem to support cgo + race mode by default.

For #73788.

Cq-Include-Trybots: luci.golang.try:gotip-freebsd-amd64-race
Change-Id: I6a6a636c06176ca746548d0588283b1429d7c6d5
Reviewed-on: https://go-review.googlesource.com/c/go/+/674160
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>