net/http: skip failing test on windows-amd64-longtest builder

bradfitz is actively thinking about a proper fix.
In the meantime, skip the test to suss out any other failures in the builder.

Updates #35122

Change-Id: I9bf0640222e3d385c1a3e2be5ab52b80d3e8c21a
Reviewed-on: https://go-review.googlesource.com/c/go/+/203500
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/transport_test.go

@@ -22,6 +22,7 @@ import (
 	"fmt"
 	"go/token"
 	"internal/nettrace"
+	"internal/testenv"
 	"io"
 	"io/ioutil"
 	"log"
@@ -2354,6 +2355,9 @@ func TestCancelRequestWithChannel(t *testing.T) {
 }
 
 func TestCancelRequestWithChannelBeforeDo_Cancel(t *testing.T) {
+	if os.Getenv("GO_BUILDER_NAME") == "windows-amd64-longtest" {
+		testenv.SkipFlaky(t, 35122)
+	}
 	testCancelRequestWithChannelBeforeDo(t, false)
 }
 func TestCancelRequestWithChannelBeforeDo_Context(t *testing.T) {