pybricksdev.connections.pybricks: Set callback before sending subscribe

This makes sure that the initial status update will be handled
and not dropped. This message contains important information such as
the currently active program slot.

Suggested-by: David Lechner <david@pybricks.com>

Author: ArcaneNibble

pybricksdev/connections/pybricks.py

@@ -947,8 +947,8 @@ async def write_gatt_char(self, uuid: str, data, response: bool) -> None:
         await self._send_message(bytes([PybricksUsbOutEpMessageType.COMMAND]) + data)
 
     async def start_notify(self, uuid: str, callback: Callable) -> None:
-        await self._send_message(bytes([PybricksUsbOutEpMessageType.SUBSCRIBE, 1]))
         self._notify_callbacks[uuid] = callback
+        await self._send_message(bytes([PybricksUsbOutEpMessageType.SUBSCRIBE, 1]))
 
     async def _monitor_usb(self):
         loop = asyncio.get_running_loop()