syscall: add another output for TestGroupCleanupUserNamespace

Fixes #16303.

Change-Id: I2832477ce0117a66da53ca1f198ebb6121953d56
Reviewed-on: https://go-review.googlesource.com/24833
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/syscall/exec_linux_test.go b/src/syscall/exec_linux_test.go
index cb24c59..aaffa06 100644
--- a/src/syscall/exec_linux_test.go
+++ b/src/syscall/exec_linux_test.go
@@ -238,6 +238,7 @@
 		"uid=0(root) gid=0(root) groups=0(root)",
 		"uid=0(root) gid=0(root) groups=0(root),65534(nobody)",
 		"uid=0(root) gid=0(root) groups=0(root),65534(nogroup)",
+		"uid=0(root) gid=0(root) groups=0(root),65534",
 	}
 	for _, e := range expected {
 		if strOut == e {