From all I could find out, there can be only one deploy key configured under circleci.com/gh/{user}/{repo}/edit#checkout. I need to checkout from a second repository, and a github read-only deploy key would be perfect for that.
Is there a technical limitation that prevents CircleCI from allowing us to add a second deploy key to the same project?
User keys are not acceptable in my case. Machine user keys neither due to my organisation policies.