Update test suite for Ruby 2.7.2 and JRuby

[HarlemSquirrel]

Closes actions/toolkit#58

It looks like we cannot yet allow failures in GH actions like we can in Travis. See actions/runner#2347
For now we can run our basic specs with Ruby head since it seems Active Record is broken there.

• Fix specs for Ruby 2.7.2
• Add Ruby head to GH CI
• Add JRuby to GH CI
• Switch from actions/setup-ruby to the more active https://github.com/ruby/setup-ruby

[swiknaba]

actually, GitHub actions does have the experimental flag, which essentially is the same as "allowed failures" from Travis: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#example-including-new-combinations

[HarlemSquirrel]

@swiknaba that appears to be just another way to use continue-on-error but we can try it.

[swiknaba]

@swiknaba that appears to be just another way to use continue-on-error but we can try it.

Indeed, I think you're right.