cmd/go: ensure the correct line number is displayed when using TB.Helper

cmd/go: ensure the correct line number is displayed when using TB.Helper

Fixes #26995

Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest-race,gotip-linux-386-longtest,gotip-windows-amd64-longtest
Change-Id: If3b68002d205fe985a692b69f5d7e0d2f20a7bd6
Reviewed-on: https://go-review.googlesource.com/c/go/+/540016
TryBot-Bypass: Bryan Mills <bcmills@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>