tsnet: skip a 30s long flaky-ish test on macOS

Updates #17805

Change-Id: I540f50d067eee12e430dfd9de6871dc784fffb8a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tsnet/tsnet_test.go

@@ -275,6 +275,9 @@ func TestDialBlocks(t *testing.T) {
 }
 
 func TestConn(t *testing.T) {
+	if runtime.GOOS == "darwin" {
+		t.Skip("slow on macOS: https://github.com/tailscale/tailscale/issues/17805")
+	}
 	tstest.ResourceCheck(t)
 	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 	defer cancel()