chore(deps): update actions/upload-artifact action to v6

Author: renovate[bot]

.github/workflows/build-example.yml

@@ -54,7 +54,7 @@ jobs:
         run: flutter build apk --no-shrink
 
       - name: Upload APK
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         if: ${{ matrix.channel == 'stable' }}
         with:
           name: app