fix(example): align parameter names with the latest function definition for gdino (#40369)

Author: developer0hye

docs/source/en/model_doc/grounding-dino.md

@@ -70,7 +70,7 @@ Here's how to use the model for zero-shot object detection:
 >>> results = processor.post_process_grounded_object_detection(
 ...     outputs,
 ...     inputs.input_ids,
-...     box_threshold=0.4,
+...     threshold=0.4,
 ...     text_threshold=0.3,
 ...     target_sizes=[image.size[::-1]]
 ... )