ci(security): upgrade artifact upload action

.github/workflows/security-governance.yml

@@ -38,7 +38,7 @@ jobs:
 
       - name: Upload security audit artifacts
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: security-audit-report
           path: security-reports/

tests/security-governance.test.cjs

@@ -26,7 +26,7 @@ test('security governance workflow enforces npm audit policy and uploads reports
 
   assert.match(workflow, /name:\s+Security Governance/);
   assert.match(workflow, /run:\s+npm run security:audit/);
-  assert.match(workflow, /actions\/upload-artifact@v4/);
+  assert.match(workflow, /actions\/upload-artifact@v6/);
   assert.match(workflow, /cron:\s+'31 17 \* \* 1'/);
 });