ssh/test: skip TestSSHCLIAuth on Windows

It's failing with a file permissions error:

sign_and_send_pubkey: signing using rsa-sha2-512 SHA256:Anr3LjZK8YVpjrxu79myrW9Hrb/wpcMNpVvTq/RcBm8\r\nBad permissions. Try removing permissions for user: UNKNOWN\\\\UNKNOWN (S-1-15-2-2) on file C:/b/s/w/ir/x/t/TestSSHCLIAuth1586735692/001/rsa.

For golang/go#64403

Change-Id: Iece8eac4a1ac349f9f7a273ac7389315cb96568e
Cq-Include-Trybots: luci.golang.try:x_crypto-gotip-windows-amd64-longtest,x_crypto-go1.21-windows-amd64-longtest,x_crypto-go1.20-windows-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/545135
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Nicola Murino <nicola.murino@gmail.com>
Auto-Submit: Heschi Kreinick <heschi@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

ssh/test/sshcli_test.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
 	"testing"
 
 	"golang.org/x/crypto/internal/testenv"
@@ -34,6 +35,9 @@ func sshClient(t *testing.T) string {
 }
 
 func TestSSHCLIAuth(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skipf("always fails on Windows, see #64403")
+	}
 	sshCLI := sshClient(t)
 	dir := t.TempDir()
 	keyPrivPath := filepath.Join(dir, "rsa")