app.py: reduce allowed concurrency

app.py

@@ -324,4 +324,4 @@ with gr.Blocks(css=css) as demo:
                                                                                       width, height, cfg_scale],
                                       concurrency_limit=32)
 
-demo.queue(max_size=40, api_open=False).launch(max_threads=128, show_api=False)
+demo.queue(max_size=20, api_open=False).launch(max_threads=40, show_api=False)