test: updated for each to for of in test file

PR-URL: https://github.com/nodejs/node/pull/50308
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/parallel/test-http-client-default-headers-exist.js

@@ -45,12 +45,12 @@ const server = http.createServer(common.mustCall((req, res) => {
          `${req.method} was an unexpected method`);
 
   const requestHeaders = Object.keys(req.headers);
-  requestHeaders.forEach((header) => {
+  for (const header of requestHeaders) {
     assert.ok(
       expectedHeaders[req.method].includes(header.toLowerCase()),
       `${header} should not exist for method ${req.method}`
     );
-  });
+  }
 
   assert.strictEqual(
     requestHeaders.length,