[repo] replace old Helm stable with Bitnami

Per https://helm.sh/blog/new-location-stable-incubator-charts/ the
previous location used here is now unavailable, breaking releases.

We furthermore no longer actually use the dependency in the old repo in
the actual chart, so changing this to the Bitnami repo rather than the
new Helm repo.

.github/workflows/main.yaml

@@ -58,7 +58,7 @@ jobs:
 
       - name: Add dependency chart repos
         run: |
-          helm repo add stable https://kubernetes-charts.storage.googleapis.com/
+          helm repo add bitnami https://charts.bitnami.com/bitnami
 
       - name: Run chart-releaser
         uses: helm/[email protected]