engine: resources: print: Add missing Recvable trait

We we're receiving values, but we forgot to list the trait. This caused
an intentional engine panic, but is easily fixed :)

engine/resources/print.go

@@ -34,6 +34,7 @@ func init() {
 type PrintRes struct {
 	traits.Base // add the base methods without re-implementation
 	traits.Groupable
+	traits.Recvable
 	traits.Refreshable
 
 	init *engine.Init