ci: add go build check to GitHub Actions

[bobheadxi]

This PR ensures a go build ./... step exists in GitHub Actions CI.

• If a build step already existed (direct or via goreleaser/make), no changes were made.
• If workflows existed but lacked a build step, one was added to the most appropriate workflow.
• If no workflows existed at all, a new go-build.yml workflow was created.

The workflow runs on every push to every branch.

Hatched by a Sourcegraph egg.