cmd/go: skip TestBinaryOnlyPackages until it's fixed

Updates #25784

Change-Id: I638eab82b026d3df89da532b5cc3f5c06b02d6c8
Reviewed-on: https://go-review.googlesource.com/117075Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/go_test.go

@@ -4217,6 +4217,7 @@ func TestFatalInBenchmarkCauseNonZeroExitStatus(t *testing.T) {
 }
 
 func TestBinaryOnlyPackages(t *testing.T) {
+	t.Skip("known failing test; see golang.org/issue/25784")
 	tooSlow(t)
 
 	tg := testgo(t)