test: replace callback functions with arrow functions

PR-URL: #24432
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

test/parallel/test-http-client-timeout-option-with-agent.js

@@ -24,7 +24,7 @@ const server = http.createServer(() => {
  // Never respond.
 });
 
-server.listen(0, options.host, function() {
+server.listen(0, options.host, () => {
  doRequest();
 });
 
@@ -50,7 +50,7 @@ function doRequest() {
  }));
  req.end();
 
- setTimeout(function() {
+ setTimeout(() => {
  req.destroy();
  assert.strictEqual(timeout_events, 1);
  // Ensure the `timeout` event fired only once.