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

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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]

🙏🏿