chore: update actions/upload-artifact action to v6

Author: renovate[bot]

.github/workflows/gradle.yml

@@ -65,7 +65,7 @@ jobs:
         run: bash ./gradlew build
 
       - name: Upload build artifacts
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: build-artifacts
           path: build/libs/*.jar