Fix missing masks for nearest scheme

[bouweandela]

Closes #368

[codecov]

Codecov Report

Attention: Patch coverage is 96.90722% with 3 lines in your changes missing coverage. Please review.

Project coverage is 98.94%. Comparing base (fdd2051) to head (83cf362).

Files	Patch %	Lines
esmf_regrid/esmf_regridder.py	93.75%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #369      +/-   ##
==========================================
+ Coverage   98.92%   98.94%   +0.01%     
==========================================
  Files          37       37              
  Lines        4196     4265      +69     
==========================================
+ Hits         4151     4220      +69     
  Misses         45       45              

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