fix: add missing build_runner step to flutter.yml workflow (#375)

Author: Catrya

.github/workflows/flutter.yml

@@ -25,6 +25,9 @@ jobs:
       - name: Install dependencies
         run: flutter pub get
 
+      - name: Generate required files
+        run: dart run build_runner build -d
+
       - name: Generate localizations
         run: flutter gen-l10n