Run golangci-lint in CI

See https://golangci-lint.run

This has already helped uncover some issues, and we should make more use
of it. Currently we have to disable one of the default lints, as we have
a lot of issues it complains about. I plan to address those one by one
and enable it. Until then, put this in place to make sure we don't
re-introduce any of the issues we've eliminated so far.

.builds/alpine.yml: upgrade to 3.22

.builds/alpine.yml: upgrade to Alpine 3.20

Update and simplify build manifest

Alpine 3.14 uses Go 1.16, but go.mod says 1.17. Also, no external
repository should be required for core-go.

.builds/alpine.yml: upgrade to 3.14

.builds/alpine.yml: tune verbosity down

.builds/alpine.yml: run tests

Initial commit