If you hit this error at the beginning of 2020 most probably you do have dependency in your chart that points to deprecated repo.
You must updated URI in charts.yaml (or requirements.yaml)
| Name | Old Location | New Location |
|---|---|---|
| stable | https://kubernetes-charts.storage.googleapis.com | https://charts.helm.sh/stable |
| incubator | https://kubernetes-charts-incubator.storage.googleapis.com | https://charts.helm.sh/incubator |
Reference: https://helm.sh/blog/new-location-stable-incubator-charts/