ci: fix output directory for example build

Author: cybex-dev

.github/workflows/flutter_web-build-deploy.yml

@@ -38,7 +38,7 @@ jobs:
         run: flutter config --enable-web
 
       - name: Create web build with release mode
-        run: cd ./example; flutter build web --release --target=lib/main.dart
+        run: cd ./example; flutter build web --release --target=lib/main.dart --output=build/web
 
       - name: Archive Production Artifact
         uses: actions/upload-artifact@v4