Earlier quoted context omitted.
Both Travis and Circle automatically install a deploy key into the project. It doesn't require additional machine users.
That's fine if you have a single repo, but CI normally needs to access lots of different repos. GitHub's documentation describes why you need machine users for anything but the most trivial deployment. https://developer.github.com/guides/managing-deploy-keys/ It's also what GitHub does internally.
This is shortsighted on their part, I hope they pay attention.