lib: replace var with let

PR-URL: #30381
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@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/v8_prof_processor.js

@@ -18,7 +18,7 @@ const scriptFiles = [
   'internal/deps/v8/tools/SourceMap',
   'internal/deps/v8/tools/tickprocessor-driver'
 ];
-var script = '';
+let script = '';
 
 scriptFiles.forEach((s) => {
   script += internalBinding('natives')[s] + '\n';