GH-98407: fix test_kill_issue43884 to not leak child processes (GH-98491)

(cherry picked from commit 3b2724a)

Co-authored-by: Kumar Aditya <[email protected]>

Author: miss-islington

Lib/test/test_asyncio/test_subprocess.py

@@ -184,7 +184,10 @@ def test_kill(self):
             self.assertEqual(-signal.SIGKILL, returncode)
 
     def test_kill_issue43884(self):
-        blocking_shell_command = f'{sys.executable} -c "import time; time.sleep(100000000)"'
+        if sys.platform == 'win32':
+            blocking_shell_command = f'{sys.executable} -c "import time; time.sleep(100000000)"'
+        else:
+            blocking_shell_command = 'sleep 1; sleep 1'
         creationflags = 0
         if sys.platform == 'win32':
             from subprocess import CREATE_NEW_PROCESS_GROUP