Update actions/upload-artifact action to v3

Author: renovate-bot

.github/workflows/flutter.yml

@@ -50,7 +50,7 @@ jobs:
         run: flutter build apk --no-shrink
 
       - name: Upload APK
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v3
         with:
           name: app-${{ matrix.flutter-channel }}
           path: build/app/outputs/apk/release/app-release.apk