bpo-34040, multiprocessing: Fix test_forkserver_sigkill() (GH-8081)

Fix test_forkserver_sigkill() of test_multiprocessing_forkserver:
give more time to the first child process to complete, double the
sleep in the parent process.

Reduce also the child process sleep from 1000 ms to 500 ms, to not change
the total duration of the test.

Lib/test/_test_multiprocessing.py

@@ -651,13 +651,17 @@ class _TestProcess(BaseTestCase):
         from multiprocessing.forkserver import _forkserver
         _forkserver.ensure_running()
 
+        # First process sleeps 500 ms
+        delay = 0.5
+
         evt = self.Event()
-        proc = self.Process(target=self._sleep_and_set_event, args=(evt, 1.0))
+        proc = self.Process(target=self._sleep_and_set_event, args=(evt, delay))
         proc.start()
 
         pid = _forkserver._forkserver_pid
         os.kill(pid, signum)
-        time.sleep(1.0)  # give it time to die
+        # give time to the fork server to die and time to proc to complete
+        time.sleep(delay * 2.0)
 
         evt2 = self.Event()
         proc2 = self.Process(target=self._sleep_and_set_event, args=(evt2,))