http: http_incoming rename var to let and const

PR-URL: #30285
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@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/_http_incoming.js

@@ -126,7 +126,7 @@ IncomingMessage.prototype.destroy = function destroy(error) {
 IncomingMessage.prototype._addHeaderLines = _addHeaderLines;
 function _addHeaderLines(headers, n) {
   if (headers && headers.length) {
-    var dest;
+    let dest;
     if (this.complete) {
       this.rawTrailers = headers;
       dest = this.trailers;
@@ -135,7 +135,7 @@ function _addHeaderLines(headers, n) {
       dest = this.headers;
     }
 
-    for (var i = 0; i < n; i += 2) {
+    for (let i = 0; i < n; i += 2) {
       this._addHeaderLine(headers[i], headers[i + 1], dest);
     }
   }