main.star: add go-internal mod presubmit

Change-Id: I4567aeb34d2b56e69d98961f6c78ea4319b3f8b9
Reviewed-on: https://go-review.googlesource.com/c/build/+/805380
Auto-Submit: Roland Shoemaker <roland@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
3 files changed