http2: change var to let compact.js

PR-URL: #30392
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
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/internal/http2/compat.js

@@ -522,7 +522,7 @@ class Http2ServerResponse extends Stream {
   addTrailers(headers) {
     const keys = Object.keys(headers);
     let key = '';
-    for (var i = 0; i < keys.length; i++) {
+    for (let i = 0; i < keys.length; i++) {
       key = keys[i];
       this.setTrailer(key, headers[key]);
     }
@@ -606,7 +606,7 @@ class Http2ServerResponse extends Stream {
     if (headers === undefined && typeof statusMessage === 'object')
       headers = statusMessage;
 
-    var i;
+    let i;
     if (Array.isArray(headers)) {
       for (i = 0; i < headers.length; i++) {
         const header = headers[i];