Gitlab-runner does not authenticate to google registry anymore


im using gitlab community edition version 12.7.2 and used a private google registry image from in my pipeline jobs. This worked until I upgraded my gitlab-runner to version 12.7.1.
It seems that the runner does not receive the DOCKER_AUTH_CONFIG variable anymore.

I tried some things to get this up and running again (e.g. add DOCKER_AUTH_CONFIG to the gitlab-runner/config.toml, downgrade to previous version), but I always receive this error:
ERROR: Preparation failed: Error response from daemon: unauthorized: You don’t have the needed permissions to perform this operation, and you may have invalid credentials. To authenticate your request, follow the steps in: (executor_docker.go:188:0s)

At the moment I’m totally lost and have no idea, why this happens. Anyone can help me out here?