集計結果がマイナスになることがある事象を修正

[codecov-commenter]

Codecov Report

Merging #131 (e4a71cc) into main (25fbb59) will decrease coverage by 0.05%. The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main     #131      +/-   ##
==========================================
- Coverage   50.89%   50.85%   -0.05%     
==========================================
  Files         123      123              
  Lines        2411     2407       -4     
==========================================
- Hits         1227     1224       -3     
+ Misses       1184     1183       -1     

Flag	Coverage Δ
unittests	50.85% <100.00%> (-0.05%)	:arrow_down:

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Files Changed	Coverage Δ
...grimage/update_pilgrimage_progress_interactor.dart	91.76% <100.00%> (+0.75%)	:arrow_up: