bpo-37531: regrtest now catchs ProcessLookupError (GH-16827)

bpo-37531: regrtest now catchs ProcessLookupError (GH-16827) · python/cpython@a661392

Original file line number	Diff line number	Diff line change
`@@ -152,6 +152,11 @@ def _kill(self):`
`152`	`152`	`print(f"Kill {self}", file=sys.stderr, flush=True)`
`153`	`153`	`try:`
`154`	`154`	`popen.kill()`
	`155`	`+except ProcessLookupError:`
	`156`	`+# Process completed, the TestWorkerProcess thread read its exit`
	`157`	`+# status, but Popen.send_signal() read the returncode just before`
	`158`	`+# Popen.wait() set returncode.`
	`159`	`+pass`
`155`	`160`	`except OSError as exc:`
`156`	`161`	`print_warning(f"Failed to kill {self}: {exc!r}")`
`157`	`162`