[Tests] CI Test Matrix

Our CI tests should be able to test the following:
* Various versions of Ember
* Various versions of Ember CLI
* Various versions of glimmer
* Various versions of ember-engines
* Various versions of ember-cli-htmlbars

This might require moving to github actions.

Start by inspecting the repository's current CI configuration and test entry points. Map how dependency versions are currently selected, then define a matrix covering the requested Ember, Ember CLI, glimmer, ember-engines, and ember-cli-htmlbars versions; done means CI runs the supported combinations reliably, potentially through GitHub Actions.

Written by the indexing model from the issue text.