net: skip TestDialCancel on darwin-arm64

We're turning up Macs in a network environment that clashes with this
test. I don't think it's critical to get it working, so skip it.

For #49149.

Change-Id: I925e3ecc5356c4cefd208bdcff3d98021215d0b4
Reviewed-on: https://go-review.googlesource.com/c/go/+/402181
Reviewed-by: Alex Rakoczy <[email protected]>
Run-TryBot: Heschi Kreinick <[email protected]>
Auto-Submit: Heschi Kreinick <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: heschi

src/net/dial_test.go

@@ -758,6 +758,12 @@ func TestDialerKeepAlive(t *testing.T) {
 func TestDialCancel(t *testing.T) {
 	mustHaveExternalNetwork(t)
 
+	if strings.HasPrefix(testenv.Builder(), "darwin-arm64") {
+		// The darwin-arm64 machines run in an environment that's not
+		// compatible with this test.
+		t.Skipf("builder %q gives no route to host for 198.18.0.0", testenv.Builder())
+	}
+
 	blackholeIPPort := JoinHostPort(slowDst4, "1234")
 	if !supportsIPv4() {
 		blackholeIPPort = JoinHostPort(slowDst6, "1234")