fix(argo-workflows): Avoid "namespace: null" when singleNamespace is true (#1154)

Signed-off-by: darklore <zodiac.brave.story@gmail.com>

charts/argo-workflows/templates/controller/workflow-rb.yaml

@@ -5,7 +5,9 @@ apiVersion: rbac.authorization.k8s.io/v1
 kind: RoleBinding
 metadata:
   name: {{ template "argo-workflows.fullname" $ }}-workflow
-  namespace: {{ $namespace }}
+    {{- with $namespace }}
+  namespace: {{ . }}
+    {{- end }}
 roleRef:
   apiGroup: rbac.authorization.k8s.io
   kind: Role