* Switch from Travis CI to GitHub Actions

Travis CI no longer works for ogórek and https://travis-ci.org/kisielk/og-rek
returns "not found".

-> Switch to GitHub Actions to fix CI.

We loose CI coverage for "go tip" as specifying "tip" Go version in
actions/setup-go is not supported out of the box:

https://github.com/actions/setup-go/issues/21

Maybe in 201x it was relevant to test wrt go tip, but nowdays I think
this is no longer much needed.

* CI += go1.16 - go1.22

Add CI coverage for all releases past go1.15 that we had before.