Checking the thread you linked, it seems docker-in-docker is not supported on GitHub actions at the moment. I tried searching for GitLab support but couldn’t find anything that claimed support for it so my guess is it’s the same. DinD is required for preloading. However this user has made preloading work on actions with a slightly different approach: Balena Preload on Github Actions - #15 by pcorbel
I suggest you take a look at it and let us know how it goes!