Quoting here, for anyone who may need it: actions/runner#1056 (comment)

It would be great if there were a purely ssh solution that didn't depend on the GUI at all. In the meantime, this can be helpful: go to System Preferences -> Users and Groups -> Login Options -> Automatic Login, and set the 'runner' or 'gha' user to login automatically. Reboot. The user will login at boot time and the services will start.