src: fix env var TZ test

In some CI environments the TZ env var is set. Since a .env file won't
override that, we need to create an env where the test can still run by
deleting the TZ variable.

test/parallel/test-dotenv-node-options.js

@@ -48,10 +48,15 @@ describe('.env supports NODE_OPTIONS', () => {
     const code = `
       require('assert')(new Date().toString().includes('Hawaii'))
     `.trim();
+    // Some CI environments set TZ. Since an env file doesn't override existing
+    // environment variables, we need to delete it and then pass the env object
+    // as the environment to spawnPromisified.
+    const env = { ...process.env };
+    delete env.TZ;
     const child = await common.spawnPromisified(
       process.execPath,
       [ `--env-file=${relativePath}`, '--eval', code ],
-      { cwd: __dirname },
+      { cwd: __dirname, env },
     );
     assert.strictEqual(child.stderr, '');
     assert.strictEqual(child.code, 0);