In PR#24804 the step size was changed to match the step size
of the device that HomeKit is controlling. Since HomeKit
is always working in TEMP_CELSIUS and the step size is based on
the Home Assistant units setting, we were mixing data with different
units of measure when Home Assistant was using imperial units.
This regression presented the symptom that setting the
temperature to 73F would result in 74F. Other values are affected
where the math doesn't happen to work out.
HomeKit currently has a default of 0.1 in the spec and the override
of this value has been removed.
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