prevent testing lib from being compiled in (#4742)

* remove testing dep from fsondisk

* code review

kyaml/filesys/fsondisk_unix.go

@@ -0,0 +1,15 @@
+// Copyright 2022 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+//go:build !windows
+// +build !windows
+
+package filesys
+
+import (
+	"path/filepath"
+)
+
+func getOSRoot() (string, error) {
+	return string(filepath.Separator), nil
+}