Be consistent and do not rely on asserts being enabled

Author: duaneg

Lib/test/mp_preload_flush.py

@@ -3,7 +3,8 @@
 
 modname = 'preloaded_module'
 if __name__ == '__main__':
-    assert modname not in sys.modules
+    if modname in sys.modules:
+        raise AssertionError(f'{modname!r} is not in sys.modules')
     multiprocessing.set_start_method('forkserver')
     multiprocessing.set_forkserver_preload([modname])
     for _ in range(2):