cmd/go: disable failing TestGoGetInsecure

Update #15410

Change-Id: Iad3f2639aa7a67b11efc35a629e1893f7d87b957
Reviewed-on: https://go-review.googlesource.com/22430
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/go_test.go

@@ -2360,6 +2360,8 @@ func TestIssue4210(t *testing.T) {
 func TestGoGetInsecure(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
 
+	t.Skip("golang.org/issue/15410")
+
 	tg := testgo(t)
 	defer tg.cleanup()
 	tg.makeTempdir()