test: move http timeout test to parallel

test-http-client-timeout-option-with-agent no longer checks that the
timeout happens within a certain tolerance so it can be moved to the
parallel test suite.

PR-URL: #22403
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: Trott