Skip folders that aren't charts

[steven-sheehy]

Saving 4 charts
Downloading loki-stack from repo https://grafana.github.io/loki/charts
Downloading prometheus-adapter from repo https://kubernetes-charts.storage.googleapis.com/
Downloading prometheus-operator from repo https://kubernetes-charts.storage.googleapis.com
Downloading traefik from repo https://containous.github.io/traefik-helm-chart
Deleting outdated charts
Packaging helm chart in directory hedera-mirror-common
helm package hedera-mirror-common --destination ../output
Successfully packaged chart and saved it to: ../output/hedera-mirror-common-0.4.0.tgz
Resolving helm chart dependency in directory hedera-mirror-grpc
helm dependency update
Packaging helm chart in directory hedera-mirror-grpc
helm package hedera-mirror-grpc --destination ../output
Successfully packaged chart and saved it to: ../output/hedera-mirror-grpc-0.4.0.tgz
Resolving helm chart dependency in directory hedera-mirror-importer
helm dependency update
Packaging helm chart in directory hedera-mirror-importer
helm package hedera-mirror-importer --destination ../output
Successfully packaged chart and saved it to: ../output/hedera-mirror-importer-0.4.0.tgz
Resolving helm chart dependency in directory hedera-mirror-rest
helm dependency update
Packaging helm chart in directory hedera-mirror-rest
helm package hedera-mirror-rest --destination ../output
Successfully packaged chart and saved it to: ../output/hedera-mirror-rest-0.4.0.tgz
Resolving helm chart dependency in directory marketplace
helm dependency update
Error: validation: chart.metadata is required
##[error]The process 'helm' failed with exit code 1

We have a folder in the charts directory that is related to the charts but is not actually a chart. It would be nice if directories without a Chart.yaml could be ignored.