cmd/go: add more tests for GOAUTH's user provided authenticator
For #26232
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest
Change-Id: I4b6eb63d4c1d71983e1ae764a6a38744a5f01317
Reviewed-on: https://go-review.googlesource.com/c/go/+/635255
Auto-Submit: Sam Thanawalla <samthanawalla@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Matloob <matloob@golang.org>