test: fix dangerous .map in test/parallel/test-http-set-trailers.js

PR-URL: #43087
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Zeyu "Alex" Yang <himself65@outlook.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

test/parallel/test-http-set-trailers.js

@@ -96,7 +96,7 @@ const server = http.createServer((req, res) => {
 });
 server.listen(0, () => {
   Promise.all([testHttp10, testHttp11, testClientTrailers]
-    .map(util.promisify)
+    .map((f) => util.promisify(f))
     .map((f) => f(server.address().port)))
     .then(() => server.close());
 });