fix: docker auth for docker.io images

Author: LaurentGoderre

docker_auth.go

@@ -42,6 +42,10 @@ func dockerImageAuth(ctx context.Context, image string, configs map[string]regis
 	defaultRegistry := defaultRegistryFn(ctx)
 	reg := core.ExtractRegistry(image, defaultRegistry)
 
+	if reg == "docker.io" {
+		reg = defaultRegistry
+	}
+
 	if cfg, ok := getRegistryAuth(reg, configs); ok {
 		return reg, cfg, nil
 	}