In case you have never used it, https://app.codecov.io/ can watch your GitHub repo and run tests + coverage. There's a nice UI to then see the coverage % for each folder and also whether a PR or commit is increasing or decreasing coverage.

If I recall correctly, there's zero configuration needed for Go projects. You can be up and running in minutes.

I think Codecov is free for open source projects and paid for private repos, someone more knowledgeable can chime in.