I don’t see the option anywhere, nor can I locate an announcement of any related change, but I tried an old public repo of mine (which was impossible to pull without auth, so it didn’t even work inside GitHub Actions) and it seems to work now. Gotta say the documentation and communication leave a lot to be desired.
Edit: I guess I’m on grandfathered (?) GitHub Packages Docker Registry, instead of the newer GitHub Container Registry (which is still in beta?).