ssh: use reflect.TypeFor instead of reflect.TypeOf

For golang/go#60088.

Change-Id: I58994c469a2793516214ab1a0072fb6137afc46e
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/709156
Auto-Submit: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Nicola Murino <nicola.murino@gmail.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Sean Liao <sean@liao.dev>

ssh/messages.go

@@ -792,7 +792,7 @@ func marshalString(to []byte, s []byte) []byte {
 	return to[len(s):]
 }
 
-var bigIntType = reflect.TypeOf((*big.Int)(nil))
+var bigIntType = reflect.TypeFor[*big.Int]()
 
 // Decode a packet into its corresponding message.
 func decode(packet []byte) (interface{}, error) {

ssh/messages_test.go

@@ -257,7 +257,7 @@ func TestDecode(t *testing.T) {
 	userAuthSuccess, err := decode([]byte{msgUserAuthSuccess})
 	if err != nil {
 		t.Errorf("error decoding userAuthSuccessMsg")
-	} else if reflect.TypeOf(userAuthSuccess) != reflect.TypeOf((*userAuthSuccessMsg)(nil)) {
+	} else if _, ok := userAuthSuccess.(*userAuthSuccessMsg); !ok {
 		t.Errorf("error decoding userAuthSuccessMsg, unexpected %T", userAuthSuccess)
 	}
 }