Run tests as Github Action

[edsu]

Once #9 is merged we should run the unit tests with Github Actions, unless there is a strong need to use CircleCI. The tests currently exercise the Docker container as a sanity check that it is working correctly. So either the Github Action environment will need Docker, or we could test the code directly without running Docker.

We would want to create test SQS queues and a test S3 bucket, so that they don't interfere with other dev/stage/prod. The secrets in .env can be added to the Action environment in Github.

It might also make sense to update the tests to clean out the s3 bucket and todo/done queues when starting up.