Harmless warning upon cronjob completion

Just for reference, once cronjob terminates, there's a Warning event emitted on the Pod that says

```
MountVolume.SetUp failed for volume "kube-api-access-xxxxx" : object "cluster-backup"/"kube-root-ca.crt" not registered
```

This is due to upstream https://github.com/kubernetes/kubernetes/issues/105204