test: switch to object spread in common/benchmark.js

PR-URL: #30309
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: Сковорода Никита Андреевич <[email protected]>
Reviewed-By: Jiawen Geng <[email protected]>
Reviewed-By: Gireesh Punathil <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: James M Snell <[email protected]>

test/common/benchmark.js

@@ -18,7 +18,7 @@ function runBenchmark(name, args, env) {
 
   argv.push(name);
 
-  const mergedEnv = Object.assign({}, process.env, env);
+  const mergedEnv = { ...process.env, ...env };
 
   const child = fork(runjs, argv, {
     env: mergedEnv,