[ci] GHA should use a Docker container like travis/docker

Apparently we have the option to run commands inside of a Docker container:
https://stackoverflow.com/questions/57549439/how-do-i-use-docker-with-github-actions

This would unify all of the testing strategies to a single image and should cut down on installation time for things

Start by inspecting the GitHub Actions workflows and the existing Travis/Docker setup referenced in the issue, then compare their installation and test environments. Done means GitHub Actions runs its commands inside a Docker container and the testing strategies use a unified image with less installation overhead.

Written by the indexing model from the issue text.