You want CI jobs that run tests in a clean machine and leave nothing behind.
1

Make a key for CI

In the dashboard, create a key with the Create and use preset and a 30 or 90 day expiry. It can create, use and delete sandboxes, and nothing else. See CI and API keys.
2

Store it as a secret

Expose it as E2B_API_KEY with E2B_DOMAIN=compute.anonalabs.com. The stock e2b SDK works as is.
3

Create, run, kill

Create a sandbox per job, copy the repository in, run the tests, and kill the sandbox in a step that always runs. The CLI’s exec and run exit with the remote command’s exit code, so a failing test fails the job.
Next: CI and API keys has a complete GitHub Actions workflow.