[3.13] [tests] test_subprocess maybe avoid a timeout race condition? (GH-133420) (#133421)

[tests] test_subprocess maybe avoid a timeout race condition? (GH-133420)

The few buildbot failures on https://github.com/python/cpython/pull/133103
are possibly just due to racing a child process launch and exit?
(cherry picked from commit b64aa302d7bc09454ba8d5b19922ff6a4192dd96)

Co-authored-by: Gregory P. Smith <greg@krypto.org>