itkN4BiasFieldCorrectionImageFilter output discrepancy between CentOS 7 and CentOS 8

As we freesurfer team were testing the reproducibility of our reconstruction code, we observed a small difference between outputs from CentOS 7 and CentOS 8, under the same binary. Upon further inspection, we believe that the difference came from itkN4BiasFieldCorrectionImageFilter. The difference is tiny but we would still like to eliminate it if possible.

Attached please find a test code and the sample input and output image files:
[itk.zip](https://github.com/InsightSoftwareConsortium/ITK/files/5379381/itk.zip)

To run the code:
./test input.nii mask.nii output.cos7.nii

The binary we tested was compiled under CentOS 7. output.cos7.nii is the result from centOS 7 and output.cos8.nii is the result from CentOS 8. If we run our mri_diff command on the two outputs, we get this:

diffcount 15932
Volumes differ in pixel data
maxdiff 0.00003052 at 13 31 17 0

As mentioned above, the difference is tiny. But we would like to eliminate it if possible. Does anyone have any idea if this could possibly be fixed/improved?

Thanks!