Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
             matrix:
                 node-version: ["18.x", "20.x", "22.x", "24.x"]
         steps:
-            - uses: actions/checkout@v5
+            - uses: actions/checkout@v6
             - name: Use Node.js v${{ matrix.node-version }}
               uses: actions/setup-node@v6
               with: