test: remove setImmediate from timeout test

In test-http2-session-timeout, setImmediate() is used to wrap makeReq().
makeReq() is asynchronous and setImmediate() is not necessary.

Backport-PR-URL: #22850
PR-URL: #23058
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Refael Ackermann <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Sakthipriyan Vairamani <[email protected]>

test/sequential/test-http2-session-timeout.js

@@ -36,7 +36,7 @@ server.listen(0, common.mustCall(() => {
       const diff = process.hrtime(startTime);
       const milliseconds = (diff[0] * 1e3 + diff[1] / 1e6);
       if (milliseconds < serverTimeout * 2) {
-        setImmediate(makeReq);
+        makeReq();
       } else {
         server.removeListener('timeout', mustNotCall);
         server.close();