Run CI on dynamically provisioned EC2 instance

[raxod502]

Currently the CI is running on GitHub Actions. This turns out to be absolutely untenable due to data transfer costs between ECR and the public Internet (just pulling down the language images to run the tests costs on the order of $14 for a single run). What we can do instead is spin up an EC2 instance in GitHub Actions, tell it to run the CI, and then terminate it after the run completes or fails.