Update checkout action to v6

Author: huangsam

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set up Python 3.14
         uses: actions/setup-python@v6
         with: