do not terminate child process explicitly

This feature sometimes causes the main process termination. Since the
child process has been already terminated (or going to) there is no need
to terminate it manually

tests/ahriman/core/test_spawn.py

@@ -140,9 +140,7 @@ def test_run_pop(spawner: Spawn) -> None:
 
     spawner.run()
 
-    first.terminate.assert_called_once_with()
     first.join.assert_called_once_with()
-    second.terminate.assert_called_once_with()
     second.join.assert_called_once_with()
     assert not spawner.active