lib: replace var with let/const

PR-URL: #30384
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/events.js

@@ -314,7 +314,7 @@ EventEmitter.prototype.emit = function emit(type, ...args) {
   } else {
     const len = handler.length;
     const listeners = arrayClone(handler, len);
-    for (var i = 0; i < len; ++i) {
+    for (let i = 0; i < len; ++i) {
       const result = ReflectApply(listeners[i], this, args);
 
       // We check if result is undefined first because that