Gem::CIDetector

For each CI, this env suffices to indicate that we’re on that CI’s containers. (A few of them only supply a CI_NAME variable, which is also nice). And if they set “CI” but we can’t tell which one they are, we also want to know that - a bare “ci” without another token tells us as much.

Any of these being set is a reasonably reliable indicator that we are executing in a CI environment.