Fix piece image layout

[sunfish-shogi]

説明 / Description

Electron将棋の初期からあった標準の駒画像と縦横比が異なる画像を使用すると比率が強制的に変えられます。
これを画像素材の比が保たれる様に修正します。

https://github.com/sunfish-shogi/electron-shogi/issues/294#issuecomment-1602573769

修正前

修正後

チェックリスト / Checklist

• MUST
  • npm test passed
  • npm run lint was applied without warnings
  • changes of /docs/webapp not included (except release branch)
  • console.log not included (except script file)
• RECOMMENDED (it depends on what you change)
  • unit test added/updated
  • i18n

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (22832f6) 70.02% compared to head (547518a) 70.03%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #548      +/-   ##
==========================================
+ Coverage   70.02%   70.03%   +0.01%     
==========================================
  Files          79       79              
  Lines       16734    16741       +7     
  Branches     2187     2187              
==========================================
+ Hits        11718    11725       +7     
  Misses       2857     2857              
  Partials     2159     2159              

Impacted Files	Coverage Δ
src/renderer/view/primitive/BoardView.vue	77.41% <100.00%> (+0.30%)	⬆️

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.