Enhanced smoke test

[pirj]

We checked some new cops/significant changes against the repos we're working on to make sure there are no errors. I thought of adding a couple of well-known OS repos and adding CI steps to test against them.

rubocop has this option:

--fail-level SEVERITY        Minimum severity (A/R/C/W/E/F) for exit with error code.

we could use E to only fail those builds if there's an error in a cop, or Ruby fails to parse.

https://github.com/pirj/real-world-rspec is a good (but not comprehensive) source of usage examples.

~I'm in between testing against the edge or some stable/fixed branch. Maybe edge and make those CI jobs optional?~

[pirj]

Let's keep it simple - make a pre-release check of the codebase against real-world-rspec. It takes 15-20m on my machine. WDYT @bquorning ?

[bquorning]

Sounds good. We can maybe start using GitHub Actions for this? That way, we can run the check only on pull requests that change version.rb.