os/exec: use testenv.SkipFlaky in TestExtraFilesFDShuffle

Change-Id: Icc1980ea0f6363c667bf91371404a8df6ed6b8ab
Reviewed-on: https://go-review.googlesource.com/c/go/+/303950
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
diff --git a/src/os/exec/exec_test.go b/src/os/exec/exec_test.go
index c1d2a8f..d854e0d 100644
--- a/src/os/exec/exec_test.go
+++ b/src/os/exec/exec_test.go
@@ -488,7 +488,7 @@
 }
 
 func TestExtraFilesFDShuffle(t *testing.T) {
-	t.Skip("flaky test; see https://golang.org/issue/5780")
+	testenv.SkipFlaky(t, 5780)
 	switch runtime.GOOS {
 	case "windows":
 		t.Skip("no operating system support; skipping")