Add a barrier action between test run action and it's dependencies.
Run will depend on this barrier action, and the barrier action will depend on:
1. The run action's dependencies
2. The previous barrier action
This will force internal/work to schedule test run actions in-order, preventing potential goroutine starvation from
the channel locking mechanism created to force test run actions to start in-order.
Fixes #73106 #61233
Change-Id: I72e9f752f7521093f3c875eef7f2f29b2393fce9
Reviewed-on: https://go-review.googlesource.com/c/go/+/668035
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Matloob <matloob@golang.org> Reviewed-by: David Chase <drchase@google.com> Reviewed-by: Michael Matloob <matloob@google.com>