ssh/test: skip tests on darwin that fail on the darwin-amd64-longtest LUCI builder

We don't yet understand why these tests fail, but the Apple sshd seems
to have some non-trivial vendor patches, so it is plausibly a
platform-specific bug in the test. Let's skip that failure mode on the
whole platform until/unless someone has time to reproduce and
investigate the failure.

For golang/go#64959.

Cq-Include-Trybots: luci.golang.try:x_crypto-gotip-darwin-amd64-longtest,x_crypto-gotip-linux-amd64-longtest,x_crypto-gotip-windows-amd64-longtest
Change-Id: I9e43579469de3fe9329c093b5916bbed0edd3751
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/554077
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Nicola Murino <nicola.murino@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Bryan Mills <bcmills@google.com>

ssh/test/forward_unix_test.go

@@ -12,6 +12,7 @@ import (
 	"io"
 	"math/rand"
 	"net"
+	"runtime"
 	"testing"
 	"time"
 )
@@ -27,6 +28,9 @@ func testPortForward(t *testing.T, n, listenAddr string) {
 
 	sshListener, err := conn.Listen(n, listenAddr)
 	if err != nil {
+		if runtime.GOOS == "darwin" && err == io.EOF {
+			t.Skipf("skipping test broken on some versions of macOS; see https://go.dev/issue/64959")
+		}
 		t.Fatal(err)
 	}
 
@@ -122,6 +126,9 @@ func testAcceptClose(t *testing.T, n, listenAddr string) {
 
 	sshListener, err := conn.Listen(n, listenAddr)
 	if err != nil {
+		if runtime.GOOS == "darwin" && err == io.EOF {
+			t.Skipf("skipping test broken on some versions of macOS; see https://go.dev/issue/64959")
+		}
 		t.Fatal(err)
 	}
 
@@ -163,6 +170,9 @@ func testPortForwardConnectionClose(t *testing.T, n, listenAddr string) {
 
 	sshListener, err := client.Listen(n, listenAddr)
 	if err != nil {
+		if runtime.GOOS == "darwin" && err == io.EOF {
+			t.Skipf("skipping test broken on some versions of macOS; see https://go.dev/issue/64959")
+		}
 		t.Fatal(err)
 	}