Installation of GitLab-managed apps (v1) seems to fail

We have a report of installing failing due to the removal of the old stable repository, see &4695 (comment 472558257):

+ export 'HELM_HOST=localhost:44134'
+ helm init --client-only
+ tiller -listen localhost:44134 -alsologtostderr
Creating /root/.helm 
Creating /root/.helm/repository 
Creating /root/.helm/repository/cache 
Creating /root/.helm/repository/local 
Creating /root/.helm/plugins 
Creating /root/.helm/starters 
Creating /root/.helm/cache/archive 
Creating /root/.helm/repository/repositories.yaml 
Adding stable repo with URL: https://kubernetes-charts.storage.googleapis.com 
[main] 2020/12/22 16:50:37 Starting Tiller v2.16.9 (tls=false)
[main] 2020/12/22 16:50:37 GRPC listening on localhost:44134
[main] 2020/12/22 16:50:37 Probes listening on :44135
[main] 2020/12/22 16:50:37 Storage driver is ConfigMap
[main] 2020/12/22 16:50:37 Max history per release is 0
Error: error initializing: Looks like "https://kubernetes-charts.storage.googleapis.com" is not a valid chart repository or cannot be reached: Failed to fetch https://kubernetes-charts.storage.googleapis.com/index.yaml : 403 Forbidden

This was on GitLab 13.7.0

/cc @hfyngvason @nicholasklick