setup-go's built-in module cache defaults to keying only on the root
go.sum, so the infra/ module's heavy Pulumi SDK dependencies
(pulumi/sdk, pulumi-cloudflare, pulumi-gcp) re-downloaded on every run.
Set cache-dependency-path to hash both go.sum and infra/go.sum so
infra/'s deps are restored from cache. The cache warms on the first
(cold) run; the speedup lands on subsequent (warm) runs.
Closes#32
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>