prevent testing lib from being compiled in (#4742)

* remove testing dep from fsondisk

* code review

kyaml/filesys/fsondisk_windows.go

@@ -0,0 +1,18 @@
+// Copyright 2022 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys
+
+import (
+	"path/filepath"
+
+	"golang.org/x/sys/windows"
+)
+
+func getOSRoot() (string, error) {
+	sysDir, err := windows.GetSystemDirectory()
+	if err != nil {
+		return "", err
+	}
+	return filepath.VolumeName(sysDir) + `\`, nil
+}