x/build/cmd/golangbuild: TryBot fails with "no packages to test" if an x/ repo contains a module with only an OS-specific package

[bcmills]

The non-Windows TryBots are failing on CL 399834 due to the winfsnotify package, which is build-constrained to only exist on Windows.

The package has always been build-constrained to only exist on WIndows, but up until that CL it was not the only package in its module. Once it is carved out, go test ./... within that module fails with the message no packages to test (added in CL 5495055).

Since the package and module are being deleted entirely in a subsequent CL, for now we can probably just accept and ignore one CL of builder failures. (It's not ideal, but I can filter out a single broken commit during builder triage pretty easily.)

In the longer term, this might be good to fix alongside #51455 (CC @golang/release).

[gopherbot]

Change https://go.dev/cl/505578 mentions this issue: x509roots/fallback: add //go:build go1.20 to bundle.go

[gopherbot]

Change https://go.dev/cl/505635 mentions this issue: cmd/go: modify go {test,vet} to scale down to 0 packages gracefully