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

Author: renovate[bot]

.github/workflows/ci.yml

@@ -96,15 +96,15 @@ jobs:
 
       - name: Upload JAR artifact
         if: steps.env.outputs.env == 'prod'
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: castle-casters-jar
           path: ./artifacts/jar/*.jar
           retention-days: 30
 
       - name: Upload coverage report
         if: steps.env.outputs.env == 'prod'
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: coverage-report
           path: ./artifacts/coverage