cmd/go: disable TestNoteReading on dragonfly

It started failing on the dragonfly builder at an unrelated commit
(one that changed the wording in a few comments in the compiler).

Created #13364 to track this.

Change-Id: I462880bed8ff565a9950e7e185de97d43999c5e2
Reviewed-on: https://go-review.googlesource.com/17143Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/note_test.go

@@ -28,6 +28,9 @@ func TestNoteReading2K(t *testing.T) {
 }
 
 func testNoteReading(t *testing.T) {
+	if runtime.GOOS == "dragonfly" {
+		t.Skipf("TestNoteReading is broken on dragonfly - golang.org/issue/13364", runtime.GOOS)
+	}
 	tg := testgo(t)
 	defer tg.cleanup()
 	tg.tempFile("hello.go", `package main; func main() { print("hello, world\n") }`)