test: use one-off agent in http consumed timeout test

Disable connection pooling for the client request so server.close()
does not wait on an idle keep-alive socket before retrying the test.

This keeps the test focused on request timeout behavior instead of
HTTP keep-alive teardown timing.

Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com>

Author: trivikr

test/parallel/test-http-server-consumed-timeout.js

@@ -58,7 +58,8 @@ function runTest(timeoutDuration) {
   server.listen(0, common.mustCall(() => {
     const req = http.request({
       port: server.address().port,
-      method: 'POST'
+      method: 'POST',
+      agent: false,
     }, () => {
       let lastIntervalTimestamp = Date.now();
       const interval = setInterval(() => {