Fix ShutdownButton LED does not stay on after hold time has expired and shutdown is ongoing

[topas-rec]

• Fixes 🐛 | ShutdownButton LED does not stay on after hold time has expired and shutdown is ongoing #1982
• See the issue reproduction procedure and please test if you're seeing this issue, too.
• callbackFunctionHandler from ShutdownButton gets called when pushing AND releasing the button
• First call of handler sets LED to on correctly after the timeout time has expired - the second call caused by releasing the button sets the LED to off. The reason is that in that call the button is not pressed anymore and the hold time does therefor not expire.
• The handler should be called only when the button is pressed, as configured here: https://github.com/MiczFlor/RPi-Jukebox-RFID/blob/develop/components/gpio_control/GPIODevices/simple_button.py#L86
• The fix is not ideal - we should find out why the GPIO does react to falling AND rising edges, but this works and therefor better than keeping the issue
• Tested on Phoniebox

[s-martin]

Thanks for fixing this bug