add test scenarios for beta

[mansona]

In #1717 we mention that we should have some scenarios for beta, this PR is the most naive way of adding those 😂

If we're happy with the time hit on CI then we should consider just merging this 👍

Edit: since I limited beta tests to linux-only there is minimal effect on our CI times 🎉

[mansona]

As it turns out we can't merge this because we've actually hit the limit of tests on github 🙃

Strategy expansion exceeded 256 results for job 'test'

[ef4]

There's a lot of stuff that could get pruned back. Many of the tests don't really need to run in every supported ember version. It would be enough to pick a few of the end-to-end tests. Same goes for duplicating tests per OS.