test: replace function with arrow function

Replace some classic functions with arrow functions in
test-child-process-send-cb.js

PR-URL: https://github.com/nodejs/node/pull/17312
Reviewed-By: Ron Korving <ron@ronkorving.nl>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-child-process-send-cb.js

@@ -4,15 +4,15 @@ const assert = require('assert');
 const fork = require('child_process').fork;
 
 if (process.argv[2] === 'child') {
-  process.send('ok', common.mustCall(function(err) {
+  process.send('ok', common.mustCall((err) => {
     assert.strictEqual(err, null);
   }));
 } else {
   const child = fork(process.argv[1], ['child']);
-  child.on('message', common.mustCall(function(message) {
+  child.on('message', common.mustCall((message) => {
     assert.strictEqual(message, 'ok');
   }));
-  child.on('exit', common.mustCall(function(exitCode, signalCode) {
+  child.on('exit', common.mustCall((exitCode, signalCode) => {
     assert.strictEqual(exitCode, 0);
     assert.strictEqual(signalCode, null);
   }));