Add GitHub action for verifying tests

[aSemy]

This adds a GitHub action that will run the tests on every pull request or change on master. This can be really helpful to quickly validate that an incoming pull request passes

Demo here: https://github.com/aSemy/iban4j/pull/1

~WIP - I'm seeing if I can get a better test report generator~ I think I've found the best test report generator. I couldn't find a good Jacoco one though.