Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/linter.yml

@@ -6,7 +6,7 @@ jobs:
   linter:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Use Node.js
       uses: actions/setup-node@v6
     - name: Install Dependencies

.github/workflows/tester.yml

@@ -10,7 +10,7 @@ jobs:
         os: [ubuntu-latest, windows-latest, macos-latest]
       fail-fast: false
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           repository: hexojs/hexo-starter
       - name: Use Node.js