fix: Update OptionsFlow property in config_flow.py

[rootnegativ1]

When adding a new folding instance, my HA logs now show the following warning:

2024-12-21 06:10:28.977 WARNING (MainThread) [homeassistant.helpers.frame] Detected that custom integration 'foldingathomecontrol' sets option flow config_entry explicitly, which is deprecated at custom_components/foldingathomecontrol/config_flow.py, line 85: self.config_entry = config_entry. This will stop working in Home Assistant 2025.12, please create a bug report at https://github.com/eifinger/hass-foldingathomecontrol/issues

Looks like this was deprecated in November 2024 per the dev blog

[rootnegativ1]

Originally, this PR removed one of the arguments from FoldingAtHomeControlOptionsFlowHandler.__init__(), but this throws an error in test_options_flow:

def __init__(self) -> None:
    """Initialize FoldingAtHomeControl options flow."""

test_options_flow TypeError: FoldingAtHomeControlOptionsFlowHandler.__init__() takes 1 positional argument but 2 were given

When re-adding the 2nd argument but commenting out the deprecation, a different error occurs:

def __init__(self, config_entry) -> None:
    """Initialize FoldingAtHomeControl options flow."""
    #self.config_entry = config_entry

test_options_flow AttributeError: 'FoldingAtHomeControlOptionsFlowHandler' object has no attribute 'config_entry'

Both iterations of __init__() seem to run fine in HA, but I'm not sure how to handle validation testing. Looks like I'll be learning about testing in the future.