Remove forgotten deprecated parse_as_dict argument in LightningCLI test (Lightning-AI#21159)

(cherry picked from commit cdc0db4)

Author: mauvilsa

tests/tests_pytorch/test_cli.py

@@ -98,7 +98,7 @@ class _UnkArgError(Exception):
     def _raise():
         raise _UnkArgError
 
-    parser = LightningArgumentParser(add_help=False, parse_as_dict=False)
+    parser = LightningArgumentParser(add_help=False)
     parser.add_lightning_class_args(Trainer, None)
 
     monkeypatch.setattr(parser, "exit", lambda *args: _raise(), raising=True)