cluster: replace var by let in shared_handle.js

PR-URL: #30402
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/cluster/shared_handle.js

@@ -11,7 +11,7 @@ function SharedHandle(key, address, port, addressType, fd, flags) {
   this.handle = null;
   this.errno = 0;
 
-  var rval;
+  let rval;
   if (addressType === 'udp4' || addressType === 'udp6')
     rval = dgram._createSocketHandle(address, port, addressType, fd, flags);
   else