Fix flaky tests

[emilyxzhou]

The integration tests sometimes fail when executed in the Docker-based action, usually with the error message "AttributeError: CordialManager instance has no attribute '_aws_client'". Although this error is resolved upon re-running the action, the tests should be fixed so we can be sure that errors are caused by modifications to the code, and not the tests themselves.

[emilyxzhou]

This issue hasn't appeared since we've made some major changes to the CI workflow, so I'm closing it for now.

[audrow]

I saw this again when trying a different way of starting the CI. I think that the tests don't have enough time between running them, so their is some cross-contamination between tests.

[audrow]

I'm going to close this again as docker run seems to get around the flaky tests, altough I'm not sure why. We can reopen if we test failures popping up again with docker run.