fix: sassのmodern-compilerを使うように

[AmaseCocoa]

What

ビルド時にLegacy JS APIに関する警告が出る問題を修正するためにmodern-compilerを利用してscssをビルドするようにしました。

Why

Dart Sass 2.0.0でLegacy JS APIが削除される予定なため。

Additional info (optional)

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 19.71%. Comparing base (e9519b0) to head (775a766).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #14651       +/-   ##
============================================
- Coverage    41.40%   19.71%   -21.70%     
============================================
  Files         1549      716      -833     
  Lines       199468   101490    -97978     
  Branches      3623      985     -2638     
============================================
- Hits         82595    20005    -62590     
+ Misses      116276    80941    -35335     
+ Partials       597      544       -53     

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[syuilo]

🙏🏿