test: favor arrow functions for anonymous callbacks

In test-https-agent-additional-options, use arrow functions for
anonymous callbacks. Replace a use of `this` with the relevant constant.
PR-URL: #27830
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: Trott

test/parallel/test-https-agent-additional-options.js

@@ -15,7 +15,7 @@ const options = {
 minVersion: 'TLSv1.1',
 };
 
-constserver=https.Server(options,function(req,res){
+constserver=https.Server(options,(req,res)=>{
 res.writeHead(200);
 res.end('hello world\n');
 });
@@ -45,9 +45,9 @@ function variations(iter, port, cb) {
 returncommon.mustCall(cb);
 }else{
 const[key,val]=value;
-returncommon.mustCall(function(res){
+returncommon.mustCall((res)=>{
 res.resume();
-https.globalAgent.once('free',common.mustCall(function(){
+https.globalAgent.once('free',common.mustCall(()=>{
 https.get(
 Object.assign({},getBaseOptions(port),{[key]: val}),
 variations(iter,port,cb)
@@ -57,16 +57,16 @@ function variations(iter, port, cb) {
 }
 }
 
-server.listen(0,common.mustCall(function(){
-constport=this.address().port;
+server.listen(0,common.mustCall(()=>{
+constport=server.address().port;
 constglobalAgent=https.globalAgent;
 globalAgent.keepAlive=true;
 https.get(getBaseOptions(port),variations(
 updatedValues.entries(),
 port,
-common.mustCall(function(res){
+common.mustCall((res)=>{
 res.resume();
-globalAgent.once('free',common.mustCall(function(){
+globalAgent.once('free',common.mustCall(()=>{
 // Verify that different keep-alived connections are created
 // for the base call and each variation
 constkeys=Object.keys(globalAgent.freeSockets);