Change type of _FillValue

The cfchecker consistently reports the following message:

CHECKING NetCDF FILE: cdd_NORDIC-3_SMHI-UERRA-Harmonie_RegRean_v1_Gridpp_v0.9_day_yr_19601231-20181230.nc
=====================
Using CF Checker Version 4.0.0
Checking against CF Version CF-1.7
Using Standard Name Table Version 77 (2021-01-19T13:38:50Z)
Using Area Type Table Version 10 (23 June 2020)
Using Standardized Region Name Table Version 4 (18 December 2018)
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Checking variable: cdd
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INFO: Invalid Type for attribute: _FillValue <class 'numpy.float32'>

While not reported as an ERROR it seems like a simple thing to change this to a normal float32