fix: CIワークフローのコード生成コマンドを修正

- build_runnerの実行コマンドをdartからflutterに変更し、正しい環境でのコード生成を保証

Author: LibraryLibrarian

.github/workflows/ci.yaml

@@ -68,7 +68,7 @@ jobs:
       - name: Codegen verify (only latest)
         if: matrix.flutter == '3.32.x'
         run: |
-          dart run build_runner build -d --build-filter="lib/**"
+          flutter pub run build_runner build -d --build-filter="lib/**"
           git diff --exit-code || (echo 'Codegen produced changes. Please commit generated files.' && exit 1)
 
   example-android: