Update upload-artifact action to version 6 in build-test workflow

Author: brunoborges

.github/workflows/build-test.yml

@@ -92,7 +92,7 @@ jobs:
 
       - name: Upload test results for site generation
         if: success() && github.ref == 'refs/heads/main'
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: test-results-for-site
           path: |