Update the model switch part.

app.py

@@ -47,6 +47,7 @@ birefnet.eval()
 @spaces.GPU
 def predict(image, resolution, weights_file):
     global weights_path
+    global birefnet
     if weights_file != weights_path:
         # Load BiRefNet with chosen weights
         birefnet = AutoModelForImageSegmentation.from_pretrained(weights_file if weights_file is not None else 'zhengpeng7/BiRefNet', trust_remote_code=True)