If that is indeed true it would only mean that the docker container is vulnerable to a supply chain attack. You are not any more vulnerable to a vulnerability in the codebase.

If you’re using the ghcr image, to post malicious code there, the attack would have already had to compromise their github infra … which would likely result in the attacker being able to push malicious code to git or publish malicious releases. Their linux distro packages are self published via a ppa/install script, which I would assume just pull from their github releases, so a bad github release would immediately be pulled as an update by users just as fast as a container.