This test is unsurprisingly failing on the nocgo builder because
the cgo packages don't exist on those builders.
Updates golang/go#28040
Change-Id: I633b73bb48e76824645e4e8dd141fb42c9adc19f
Reviewed-on: https://go-review.googlesource.com/c/140121
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>