test: remove unnecessary await in test-watch-mode

PR-URL: nodejs#55142
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jake Yuesong Li <jake.yuesong@gmail.com>

test/sequential/test-watch-mode.mjs

@@ -225,7 +225,7 @@ describe('watch mode', { concurrency: !process.env.TEST_PARALLEL, timeout: 60_00
 
     try {
       await restart();
-      await writeFileSync(envFile, `${envKey}=value1\n${envKey2}=newValue`);
+      writeFileSync(envFile, `${envKey}=value1\n${envKey2}=newValue`);
 
       // Second restart, after env change
       const { stderr, stdout } = await restart();