Update actions checkout to v6

Author: hirokiterashima

.github/workflows/test-coverage.yml

@@ -11,7 +11,7 @@ jobs:
         node-version: [24.x]
         # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v6
       - name: Use Node.js ${{ matrix.node-version }}
         uses: actions/setup-node@v1
         with: