test: fix http agent keep-alive server hint test case 4

Node's http.Server automatically sends Keep-Alive: timeout=65 on every
keep-alive response unless keepAliveTimeout is set to 0. Case 4 assumed
no hint would be sent with a plain createServer(), which was incorrect.

Use { keepAliveTimeout: 0 } to suppress the automatic header and
correctly test the no-hint code path.

Refs: #66734
Signed-off-by: Divyanshu Sharma <divyanshu88999@gmail.com>

Author: DivyanshuX9

test/parallel/test-http-agent-keep-alive-server-hint.js

@@ -128,12 +128,16 @@ function getIdleSocket(agent) {
   }));
 }
 
-// Case 4: No Keep-Alive header from server, no agent timeout.
+// Case 4: Server sends no Keep-Alive hint (keepAliveTimeout: 0 suppresses the
+// automatic header), no agent timeout.
 // Expected: socket.timeout === 0 (no timer set — existing behaviour unchanged).
 {
-  const server = http.createServer(common.mustCall((req, res) => {
-    res.end('ok');
-  }));
+  const server = http.createServer(
+    { keepAliveTimeout: 0 },
+    common.mustCall((req, res) => {
+      res.end('ok');
+    })
+  );
 
   server.listen(0, common.mustCall(() => {
     const agent = new http.Agent({ keepAlive: true });