Run CI jobs against Puppet 7 and Ruby 3

[ahayworth]

Overview

This PR runs CI against puppet 7.3.0, testing ruby versions 2.5 - 3.0.

I first tried to refactor the CI jobs, and then got caught up in dependency hell; so I just copied the previous jobs and updated them.

Checklist

• Make sure that all of the tests pass, and fix any that don't. Just run rake in your checkout directory, or review the CI job triggered whenever you push to a pull request.
• Make sure that there is 100% test coverage by running rake coverage:spec or ignoring untestable sections of code with # :nocov comments. If you need help getting to 100% coverage please ask; however, don't just submit code with no tests.
• If you have added a new command line option, we would greatly appreciate a corresponding integration test that exercises it from start to finish. This is optional but recommended.
• If you have added any new gem dependencies, make sure those gems are licensed under the MIT or Apache 2.0 license. We cannot add any dependencies on gems licensed under GPL.
• If you have added any new gem dependencies, make sure you've checked in a copy of the .gem file into the vendor/cache directory.

[ahayworth]

cc @benburry