flutter_action.yml: fix annotations

Author: Sergey Khomushin

.github/workflows/flutter_action.yml

@@ -17,7 +17,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
-      - uses: subosito/flutter-action
+      - uses: subosito/flutter-action@v2
 
       - name: Install dependencies
         run: flutter pub get