test: change object assign to spread object

change object assign to spread object in test-npm-install.js
PR-URL: #30422
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@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>

test/parallel/test-npm-install.js

@@ -38,12 +38,12 @@ const pkgPath = path.join(installDir, 'package.json');
 
 fs.writeFileSync(pkgPath, pkgContent);
 
-const env = Object.assign({}, process.env, {
-  PATH: path.dirname(process.execPath),
-  NPM_CONFIG_PREFIX: path.join(npmSandbox, 'npm-prefix'),
-  NPM_CONFIG_TMP: path.join(npmSandbox, 'npm-tmp'),
-  HOME: homeDir,
-});
+const env = { ...process.env,
+              PATH: path.dirname(process.execPath),
+              NPM_CONFIG_PREFIX: path.join(npmSandbox, 'npm-prefix'),
+              NPM_CONFIG_TMP: path.join(npmSandbox, 'npm-tmp'),
+              HOME: homeDir,
+};
 
 exec(`${process.execPath} ${npmPath} install`, {
   cwd: installDir,