feat(github-action)!: Update actions/checkout action to v6 (#1259)

Co-authored-by: trap-renovate[bot] <138502363+trap-renovate[bot]@users.noreply.github.com>

Author: trap-renovate[bot]

.github/workflows/diff.yaml

@@ -25,7 +25,7 @@ jobs:
           rm ksops-dry-run-linux-amd64.tar.gz
 
       - name: Fetch base
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: "2"
 

.github/workflows/renovate.yaml

@@ -64,7 +64,7 @@ jobs:
           app_id: "${{ secrets.RENOVATE_APP_ID }}"
           private_key: "${{ secrets.RENOVATE_APP_PRIVATE_KEY }}"
 
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       # Renovateは別で設定が必要らしい？
       #  - name: Login to GitHub Container Registry

.github/workflows/validate.yaml

@@ -16,7 +16,7 @@ jobs:
     # Exclude duplicate execution for PRs from renovate branches
     if: ${{ !(github.event_name == 'pull_request' && startsWith(github.event.pull_request.head.ref, 'renovate/')) }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       # Simpler alternative: https://stackoverflow.com/a/73596568
       # - name: Setup to skip ksops decryption