fix dreambooth script. (#1017)

make input_args optional

examples/dreambooth/train_dreambooth.py

@@ -26,7 +26,7 @@ from transformers import CLIPTextModel, CLIPTokenizer
 logger = get_logger(__name__)
 
 
-def parse_args(input_args):
+def parse_args(input_args: None):
     parser = argparse.ArgumentParser(description="Simple example of a training script.")
     parser.add_argument(
         "--pretrained_model_name_or_path",