[CI] Count a zombie as reaped in test_run_example_terminates_timeouts

[huydhn]

• Treat the killed child as gone once it is a zombie in test_run_example_terminates_timeouts.
• On OSDC the job container's PID 1 is tail -f /dev/null, which never reaps orphans, so the child run_example kills stays a zombie and os.kill(pid, 0) still succeeds. Under linux_job_v2 PID 1 was the image's bash, which reaped it.

[pytorch-bot]

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✅ You can merge normally! (2 Unrelated Failures)

As of commit baeed8d with merge base 47bd395 ():

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Libs Tests on Linux / unittests-gym (3.10, 12.8) / linux-job (gh) (trunk failure)
  RuntimeError: Command bash /__w/_temp/exec_script failed with exit code 1
• Libs Tests on Linux / unittests-sklearn (3.10, 12.8) / linux-job (gh) (trunk failure)
  RuntimeError: Command bash /__w/_temp/exec_script failed with exit code 1

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[huydhn]

Folded into #4544.