old/netchan: disable a test with a data race on the builders for now

This is both old and experimental, so let's not make it distract
people trying to do other work in x/exp with trybot failures.

Updates golang/go#31575

Change-Id: Id14dac6404fe53a9512f5d810fd282bdc17162a8
Reviewed-on: https://go-review.googlesource.com/c/exp/+/173057
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/old/netchan/netchan_test.go b/old/netchan/netchan_test.go
index 9a7c076..03b8aa2 100644
--- a/old/netchan/netchan_test.go
+++ b/old/netchan/netchan_test.go
@@ -6,6 +6,7 @@
 
 import (
 	"net"
+	"os"
 	"strings"
 	"testing"
 	"time"
@@ -231,6 +232,9 @@
 // Test hanging up the send side of an import.
 // TODO: test hanging up the receive side of an import.
 func TestImportHangup(t *testing.T) {
+	if os.Getenv("GO_BUILDER_NAME") != "" {
+		t.Skipf("skipping test with data race on builders; see https://golang.org/issue/31575")
+	}
 	exp, imp := pair(t)
 	ech := make(chan int)
 	err := exp.Export("exportedRecv", ech, Recv)