test: add missing copyright notice

Change-Id: I2a5353203ca2958fa37fc7a5ea3f22ad4fc62b0e
Reviewed-on: https://go-review.googlesource.com/24282
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

test/fixedbugs/issue16008.go

 // errorcheck -0 -race
 
+// Copyright 2016 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.
+
 package foo
 
 const benchmarkNumNodes = 10000