FIX: Load file with mmap=False when modifying on-disk dtype

[effigies]

This causes a BusError reported in NeuroStars #4641.

[codecov]

Codecov Report

Merging #378 into master will increase coverage by 0.64%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #378      +/-   ##
==========================================
+ Coverage   39.01%   39.66%   +0.64%     
==========================================
  Files          43       43              
  Lines        4788     4788              
==========================================
+ Hits         1868     1899      +31     
+ Misses       2920     2889      -31

Flag	Coverage Δ
#reportlettests	100% <ø> (ø)	⬆️
#unittests	39.66% <100%> (+0.64%)	⬆️

Impacted Files	Coverage Δ
niworkflows/interfaces/itk.py	38.88% <100%> (+10.49%)	⬆️
niworkflows/interfaces/utils.py	41.05% <0%> (+2.62%)	⬆️
niworkflows/interfaces/fixes.py	60% <0%> (+15%)	⬆️

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[effigies]

Looking into it more, this should resolve the issue with nipreps/fmriprep#1555 after all. I had forgotten we had fixed the other one of these a bit ago.

[effigies]

@oesteban This is all set and the case is covered.