test: minor adjustments to test-http2-respond-file

PR-URL: #21098
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

test/parallel/test-http2-respond-file.js

@@ -19,7 +19,7 @@ const data = fs.readFileSync(fname);
 const stat = fs.statSync(fname);
 
 const server = http2.createServer();
-server.on('stream', (stream) => {
+server.on('stream', common.mustCall((stream) => {
   stream.respondWithFile(fname, {
     [HTTP2_HEADER_CONTENT_TYPE]: 'text/plain'
   }, {
@@ -28,9 +28,9 @@ server.on('stream', (stream) => {
       headers[HTTP2_HEADER_CONTENT_LENGTH] = stat.size;
     }
   });
-});
-server.listen(0, () => {
+}));
 
+server.listen(0, common.mustCall(() => {
   const client = http2.connect(`http://localhost:${server.address().port}`);
   const req = client.request();
 
@@ -49,4 +49,4 @@ server.listen(0, () => {
     server.close();
   }));
   req.end();
-});
+}));