Fix review comment of GitHub Copilot

Author: davidsblom

nautilus_trader/adapters/dydx/websocket/client.py

@@ -417,6 +417,12 @@ async def unsubscribe_channel(
             return
 
         if channel_id is None:
+            if len(self._subscriptions[channel]) > 1:
+                self._log.error(
+                    f"Cannot unsubscribe from {channel.value}: multiple subscriptions exist, specify channel_id",
+                )
+                return
+
             self._subscriptions.pop(channel)
         else:
             self._subscriptions[channel].remove(channel_id)