Update actions/upload-artifact action to v6

Author: renovate[bot]

.github/workflows/test.yml

@@ -32,7 +32,7 @@ jobs:
         run: go tool cover -html=coverage.out -o coverage.html
 
       - name: Upload coverage report
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: coverage-report
           path: coverage.html