Bottom decile has sign flipped on relative impact

[MaxGhenis]

For example this case has positive absolute change:

but negative relative:

This shouldn't happen since we assign negatives to the -1 decile: https://github.com/PolicyEngine/policyengine-us/blob/master/policyengine_us/variables/household/income/household/household_income_decile.py

And we use that for binning:

https://github.com/PolicyEngine/policyengine-api/blob/615a196708cf42197002928e3a660e6ed7c11d08/policyengine_api/endpoints/economy/compare.py#L125-L158