syscall: allow EINVAL in TestSCMCredentials

This can occur on NixOS.

Change-Id: I0571b0cc5345d01396dca6a4116aa1024c390a5a
Reviewed-on: https://go-review.googlesource.com/c/go/+/393437
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/syscall/creds_test.go

@@ -77,8 +77,10 @@ func TestSCMCredentials(t *testing.T) {
 			if sys, ok := err.(*os.SyscallError); ok {
 				err = sys.Err
 			}
-			if err != syscall.EPERM {
-				t.Fatalf("WriteMsgUnix failed with %v, want EPERM", err)
+			switch err {
+			case syscall.EPERM, syscall.EINVAL:
+			default:
+				t.Fatalf("WriteMsgUnix failed with %v, want EPERM or EINVAL", err)
 			}
 		}