cmd/dist: test GOFIPS140=latest rather than just the GODEBUG
GOFIPS140=latest turns on the GODEBUG by default, and it's otherwise
untested.
Change-Id: I6a6a4656ff7ad313ce2c61ee4144ad2858bd148c
Reviewed-on: https://go-review.googlesource.com/c/go/+/648819
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Daniel McCarney <daniel@binaryparadox.net> Reviewed-by: Roland Shoemaker <roland@golang.org>