move to github ci and drop support for Ember 3.4 and 3.8

[mansona]

Description

Since Travis has gone bye bye 😢 it's about time to move to github actions for CI 🎉 Hopefully this PR will achieve this.

Note: this isn't considered a breaking change even though I'm removing tests for 3.4 and 3.8 becuase they were already failing before this PR. There is a chance that we've broken semver at some point in the past but we don't know because Travis has stopped working and it's hard to figure it out 😞

Also we expect the floating dependencies test to fail, along with ember canary 👍 so we can merge even if they fail

[dcyriller]

Thanks a lot @mansona!

I'm looking at the commits on the main branch. It seems the CI has been failing for 3.8 for the first time when we merged this ember-cli upgrade. It was two PRs ago, no release has been done so far.

I am all 👍 with removing the test suite for 3.4 and 3.8. That said the last version we published was working well with these versions. This is why I think we should release a major to drop support for these versions. Is it okay by you?

[mansona]

Yes I'm happy with this being a breaking version 👍 it's safer than my proposal and that's always a good thing 😂