Have importlib.test.regrtest clear sys.path_importer_cache to make
sure finders from importlib are used instead of _frozen_importlib.
diff --git a/Lib/importlib/test/regrtest.py b/Lib/importlib/test/regrtest.py
index 9cc9ee7..a5be11f 100644
--- a/Lib/importlib/test/regrtest.py
+++ b/Lib/importlib/test/regrtest.py
@@ -12,5 +12,6 @@
 
 if __name__ == '__main__':
     __builtins__.__import__ = importlib.__import__
+    sys.path_importer_cache.clear()
 
     regrtest.main(quiet=True, verbose2=True)