test_runner: make it compatible with fake timers

Signed-off-by: Matteo Collina <hello@matteocollina.com>
PR-URL: #59272
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Chemi Atlow <chemi@atlow.co.il>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Aviv Keller <me@aviv.sh>
Reviewed-By: Paolo Insogna <paolo@cowtech.it>

Author: mcollina