Add helm env variables explicitly to pulumi Dockerfile (#4474)

CHANGELOG.md

@@ -22,6 +22,10 @@ CHANGELOG
 - Ensure generated Python module names are keyword-safe.
   [#4473](https://github.com/pulumi/pulumi/pull/4473)
 
+- Explicitly set XDG_CONFIG_HOME and XDG_CACHE_HOME env vars for helm in the
+  pulumi docker image
+  [#4474](https://github.com/pulumi/pulumi/pull/4474)
+
 - Increase the MaxCallRecvMsgSize for all RPC calls. 
   [#4455](https://github.com/pulumi/pulumi/pull/4455)
 

dist/pulumi/Dockerfile

@@ -55,6 +55,11 @@ RUN wget -q https://packages.microsoft.com/config/ubuntu/19.04/packages-microsof
     dotnet-sdk-3.1
 
 # Install Helm
+# Explicitly set env variables that helm reads to their defaults, so that subsequent calls to
+# helm will find the stable repo even if $HOME points to something other than /root
+# (e.g. in GitHub actions where $HOME points to /github/home).
+ENV XDG_CONFIG_HOME=/root/.config
+ENV XDG_CACHE_HOME=/root/.cache
 RUN curl -L https://raw.githubusercontent.com/helm/helm/master/scripts/get-helm-3 | bash && \
   helm repo add stable https://kubernetes-charts.storage.googleapis.com && \
   helm repo update