os: os_chmod_test.go: fix copyright

src/os/os_chmod_test.go

@@ -1,6 +1,10 @@
 // +build !baremetal,!js,!wasi
 
-// TODO: Move this into os_test.go (as upstream has it) when wasi supports chmod
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// TODO: Move this back into os_test.go (as upstream has it) when wasi supports chmod
 
 package os_test