Upgrade to 1.2.4 fails: X509: certificate signed by unknown authority

Hi all,
I’m trying to upgrade istio from 1.2.2 to 1.2.4 following instructions at
Upgrade steps (helm upgrade)

I downloaded the 1.2.4 release but the istio-init upgrade fails

sysop@k3s-master:~/software/istio-1.2.4$ sudo helm upgrade --install --force istio-init install/kubernetes/helm/istio-init --namespace istio-system
[sudo] password for sysop: 
Error: Get https://k3s-master:6443/api/v1/namespaces/kube-system/pods?labelSelector=app%3Dhelm%2Cname%3Dtiller: x509: certificate signed by unknown authority

What can I do?