DOCKER_REGISTRY_RELEASE_PASSWORD override DOCKER_CONFIG_FILE

Describe the bug

Since 9bb198ef

Setting credentials for DOCKER_RELEASE_IMAGE in DOCKER_CONFIG_FILE

Expected behavior

Should just work

Actual behavior

GitLab CI_REGISTRY credentials are used instead (default value of DOCKER_REGISTRY_RELEASE_PASSWORD). So docker-publish fails

Logs and/or screenshots

See content of dest-config.json

docker-publish:
  before_script:
    - !reference [.docker-scripts]
    - export BUILDTOOL_HOME=${BUILDTOOL_HOME:-$HOME}
    - cat "$BUILDTOOL_HOME/skopeo/.docker/src-config.json"
    - cat "$BUILDTOOL_HOME/skopeo/.docker/dest-config.json"