test: refactor test-http-agent-timeout-option

There is no need to establish a TCP connection. It is sufficient to
test that the listener that forwards the `'timeout'` event from the
socket to the `ClientRequest` instance is added to the socket.

PR-URL: https://github.com/nodejs/node/pull/25886


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>