test: skip test/fixedbugs/bug345.go on windows

Before the CL 115277 we did not run the test on Windows,
so let's just go back to not running the test on Windows.
There is nothing OS-specific about this test,
so skipping it on Windows doesn't seem like a big deal.

Updates #25693
Fixes #25586

Change-Id: I1eb3e158b322d73e271ef388f8c6e2f2af0a0729
Reviewed-on: https://go-review.googlesource.com/115857
Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

test/fixedbugs/bug345.go

+// +build !windows
 // errorcheckdir -n
 
-// run
 // Copyright 2011 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 ignored
+
+// TODO(ysmolsky): Fix golang.org/issue/25693 to enable on Windows.