Fix typo in function name

[justbispo]

Pretty sure _update_menu was a typo, there's no function with that name. And running udiskie in the terminal and clicking the tray icon showed the error:

Traceback (most recent call last):
  File "/usr/lib/python3.14/site-packages/udiskie/appindicator.py", line 60, in _on_show
    self._update_menu()
    ^^^^^^^^^^^^^^^^^
AttributeError: 'AppIndicatorIcon' object has no attribute '_update_menu'. Did you mean: 'update_menu'?

[coldfix]

Thank you!