[Chess] Use int8

[sotetsuk]

Action requires cast

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.95%. Comparing base (5ae5f01) to head (680dd92).
⚠️ Report is 34 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1259   +/-   ##
=======================================
  Coverage   79.95%   79.95%           
=======================================
  Files          61       61           
  Lines        5758     5758           
=======================================
  Hits         4604     4604           
  Misses       1154     1154           

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[sotetsuk]

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