lib: replaced var to let in lib/v8.js

PR-URL: #30305
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: Jiawen Geng <technicalcute@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/v8.js

@@ -165,7 +165,7 @@ function getHeapSpaceStatistics() {
   const buffer = heapSpaceStatisticsBuffer;
   updateHeapSpaceStatisticsArrayBuffer();
 
-  for (var i = 0; i < kNumberOfHeapSpaces; i++) {
+  for (let i = 0; i < kNumberOfHeapSpaces; i++) {
     const propertyOffset = i * kHeapSpaceStatisticsPropertiesCount;
     heapSpaceStatistics[i] = {
       space_name: kHeapSpaces[i],