add config for Gemini Code Assistant

[sensuikan1973]

https://developers.google.com/gemini-code-assist/docs/customize-gemini-behavior-github?hl=ja#custom-configuration

[gemini-code-assist]

Note

Gemini is unable to generate a summary for this pull request due to the file types involved not being currently supported.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.03%. Comparing base (6e7e9a0) to head (9b04e04).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2608   +/-   ##
=======================================
  Coverage   94.03%   94.03%           
=======================================
  Files          52       52           
  Lines        1476     1476           
=======================================
  Hits         1388     1388           
  Misses         88       88           

Flag	Coverage Δ
integration_test	65.44% <ø> (ø)
macos-latest	93.08% <ø> (ø)
ubuntu	93.49% <ø> (ø)
widget_test	90.38% <ø> (ø)
windows	93.49% <ø> (ø)

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