cmd/go/internal/vcs: error out if the requested repo does not support a secure protocol

cmd/go/internal/vcs: error out if the requested repo does not support a secure protocol

Fixes #63845.

Change-Id: If86d6b13d3b55877b35c087112bd76388c9404b8
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/539321
Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>