chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/pdf.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4.2.2
+        uses: actions/checkout@v6.0.0
       - name: Setup Node.js environment
         uses: actions/setup-node@v4.4.0
       - name: Install Prince

.github/workflows/spellchecker.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Code
-        uses: actions/checkout@v4.2.2
+        uses: actions/checkout@v6.0.0
 
       - name: Setup Node.js environment
         uses: actions/setup-node@v4.4.0