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

Author: renovate[bot]

.github/workflows/ci.yml

@@ -137,7 +137,7 @@ jobs:
       
       # === ARTIFACTS PHASE ===
       - name: Archive test results
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         if: always()
         with:
           name: "test-results-${{ github.run_number }}-${{ github.sha }}"