CI: migrate workflows to checkout v6 (#579)

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Enable Corepack
         run: corepack enable

.github/workflows/claude.yml

@@ -41,7 +41,7 @@ jobs:
       id-token: write
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 1
 

.github/workflows/deploy.yml

@@ -46,7 +46,7 @@ jobs:
           fi
 
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false