chore(deps): update actions/upload-artifact action to v4

Author: renovate[bot]

.github/workflows/flutter.yml

@@ -51,7 +51,7 @@ jobs:
 
       - name: Upload APK
         if: ${{ matrix.flutter-channel == 'stable' }}
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: app-${{ matrix.flutter-channel }}
           path: build/app/outputs/apk/debug/app-debug.apk