Rename output_dir argument (#5916)

Fix typo in output_dir argument: "text-inversion-model" → "dreambooth-model"

examples/dreambooth/train_dreambooth.py

@@ -300,7 +300,7 @@ def parse_args(input_args=None):
     parser.add_argument(
         "--output_dir",
         type=str,
-        default="text-inversion-model",
+        default="dreambooth-model",
         help="The output directory where the model predictions and checkpoints will be written.",
     )
     parser.add_argument("--seed", type=int, default=None, help="A seed for reproducible training.")