gh-155727: Ignore internal imports in test_attribute_completion (GH-155730)

Reader.run_hooks() imports _pyrepl._threading_handler lazily, and the
test counted it as a module imported by the completer.

Author: serhiy-storchaka

Lib/test/test_pyrepl/test_pyrepl.py

@@ -1467,7 +1467,10 @@ def test_attribute_completion(self):
                         reader = self.prepare_reader(events, namespace={})
                         output = reader.readline()
                         self.assertEqual(output, expected)
-                        new_imports = sys.modules.keys() - _imported
+                        # The reader imports its own helpers lazily.
+                        new_imports = {name for name in
+                                       sys.modules.keys() - _imported
+                                       if not name.startswith('_pyrepl.')}
                         self.assertEqual(new_imports, expected_imports)
 
     @patch.dict(sys.modules)