test: use error code rather than message in test

Use err.code checking instead of err.message checking in
test-child-process-fork-closed-channel-segfault.

PR-URL: #20859
Reviewed-By: Daniel Bevenius <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Sakthipriyan Vairamani <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>

test/parallel/test-child-process-fork-closed-channel-segfault.js

@@ -66,7 +66,7 @@ const server = net
         send(function(err) {
           // Ignore errors when sending the second handle because the worker
           // may already have exited.
-          if (err && err.message !== 'Channel closed') {
+          if (err && err.code !== 'ERR_IPC_CHANNEL_CLOSED') {
             throw err;
           }
         });