Ensure hole filling output is int

[sarthakpati]

Fixes #N.A.

Proposed Changes

• hole filling output should be int

Checklist

• I have read the CONTRIBUTING guide
• My PR is based from the current GaNDLF master
• Non-breaking change (would not break existing functionality): please provide as many details as possible for any breaking change
• Function/class source code documentation added/updated
• Code has been blacked for style consistency
• If applicable, version information has been updated in GANDLF/version.py
• If adding a git submodule, add to list of exceptions for black styling in pyproject.toml file
• Usage documentation has been updated, if appropriate
• History has been updated, if appropriate
• Tests added or modified to cover the changes; if coverage is reduced, please give explanation

[codecov]

Codecov Report

Merging #306 (daaec51) into master (d5c68a0) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #306      +/-   ##
==========================================
+ Coverage   88.36%   88.39%   +0.02%     
==========================================
  Files          84       84              
  Lines        4247     4255       +8     
==========================================
+ Hits         3753     3761       +8     
  Misses        494      494              

Flag	Coverage Δ
unittests	88.39% <100.00%> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
GANDLF/post_process/morphology.py	96.66% <100.00%> (+0.83%)	⬆️
testing/test_full.py	98.90% <100.00%> (+<0.01%)	⬆️

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