timeout: Fix performance regression using sigtimedwait #13032

Job	Run time
Style/format (ubuntu-latest, feat_os_unix)	15s
Style/lint (ubuntu-latest, all, true)	1m 58s
Style/spelling (ubuntu-latest, feat_os_unix)	1m 0s
Style/lint (windows-latest, feat_os_windows)	2m 51s
Style/lint (macos-latest, feat_os_macos)	1m 34s
Style/Python	8s
Pre-commit hooks	29s
Style/toml	10s
	8m 25s

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