fixing insecure hash function

examples/tutorial/new_api/dreambooth/train_dreambooth_colossalai.py

@@ -397,7 +397,7 @@ def main(args):
                 images = pipeline(example["prompt"]).images
 
                 for i, image in enumerate(images):
-                    hash_image = hashlib.sha1(image.tobytes()).hexdigest()
+                    hash_image = hashlib.sha256(image.tobytes()).hexdigest()
                     image_filename = class_images_dir / f"{example['index'][i] + cur_class_images}-{hash_image}.jpg"
                     image.save(image_filename)