mgmt-image-ref-report job fails "Unexpected error in get_helm_artifacts"

mgmt-image-ref-report job with this error:

{'kind': 'Pod', 'name': 'workload-cluster-operator-controller-manager-7699d5f64f-tklg4', 'namespace': 'workload-cluster-operator-system'}ERROR:__main__:Unexpected error in get_helm_artifacts (releases): 'chart'

this is a regresssion due to !6095 (merged) (the script does not know how to handle a HelmRelease which has no spec.chart.ref, and such a HelmRelease was introduced by !6095 (merged))