Update flutter-action pinned version (#1435)

Author: jtmcdole

.github/workflows/flutter_news_example.yaml

@@ -33,7 +33,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: subosito/flutter-action@v2.18.0
+      - uses: subosito/flutter-action@e938fdf56512cc96ef2f93601a5a40bde3801046
         with:
           channel: ${{matrix.channel}}
           flutter-version: "3.24.2"