fix: skip import of broken/invalid manifest list/index references

mentioned in commit 091d8138

mentioned in issue #701 (closed)

mentioned in merge request gitlab-org/build/CNG!1041 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1829 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1830 (merged)

mentioned in merge request gitlab-org/charts/gitlab!2604 (merged)

mentioned in merge request omnibus-gitlab!6181 (merged)

mentioned in merge request gitlab-development-kit!2656 (merged)