ci: remove hardcoded flutter version in publish.yaml

Signed-off-by: Shengqi Chen <[email protected]>

Author: Harry-Chen

.github/workflows/publish.yaml

@@ -1,8 +1,5 @@
 name: Publish to pub.dev
 
-env:
-  FLUTTER_VERSION: 3.38.3
-
 on:
   push:
     tags:
@@ -21,7 +18,6 @@ jobs:
         uses: flutter-actions/setup-flutter@v4
         with:
           channel: stable
-          version: ${{ env.FLUTTER_VERSION }}
           cache: true
       - name: Install dependencies
         run: flutter pub get