http2: core.js replace var with let

const has to be used in for in loop

PR-URL: #30403
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/internal/http2/core.js

@@ -582,7 +582,7 @@ function onOrigin(origins) {
   if (!session.encrypted || session.destroyed)
     return undefined;
   const originSet = initOriginSet(session);
-  for (var n = 0; n < origins.length; n++)
+  for (let n = 0; n < origins.length; n++)
     originSet.add(origins[n]);
   session.emit('origin', origins);
 }
@@ -1496,7 +1496,7 @@ class ServerHttp2Session extends Http2Session {
     let arr = '';
     let len = 0;
     const count = origins.length;
-    for (var i = 0; i < count; i++) {
+    for (let i = 0; i < count; i++) {
       let origin = origins[i];
       if (typeof origin === 'string') {
         origin = (new URL(origin)).origin;
@@ -2128,7 +2128,7 @@ function processHeaders(oldHeaders) {
   if (oldHeaders !== null && oldHeaders !== undefined) {
     const hop = hasOwnProperty.bind(oldHeaders);
     // This loop is here for performance reason. Do not change.
-    for (var key in oldHeaders) {
+    for (const key in oldHeaders) {
       if (hop(key)) {
         headers[key] = oldHeaders[key];
       }