benchmark: fix benchmark/run.js handling of --set

run.js does not work with --set as it tries to include it as
options to `fork()` rather than as part of argv for `fork()`. This
doesn't throw an error because of a quirk in `fork()` that silently
accepts arrays for options objects. This will be changing in Node.js
18.x.

PR-URL: #41334
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: Trott

benchmark/run.js

@@ -42,8 +42,7 @@ if (format === 'csv') {
   const filename = benchmarks[i];
   const child = fork(
     path.resolve(__dirname, filename),
-    cli.test ? ['--test'] : [],
-    cli.optional.set
+    cli.test ? ['--test'] : cli.optional.set
   );
 
   if (format !== 'csv') {