Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/lint.yml

@@ -12,12 +12,12 @@ jobs:
     timeout-minutes: 10
     steps:
       # プルリクエスト元リポジトリからプルリクエスト作成時のプルリクエスト先baseブランチの最新コミットを取得
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           repository: ${{ github.event.pull_request.head.repo.full_name }}
           ref: ${{ github.event.pull_request.base.sha }}
       # プルリクエスト元リポジトリからプルリクエスト用ブランチの最新コミットを取得して上書き
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           repository: ${{ github.event.pull_request.head.repo.full_name }}
           ref: ${{ github.head_ref }}

.github/workflows/sync.yml

@@ -18,7 +18,7 @@ jobs:
           app-id: ${{ secrets.APP_ID }}
           private-key: ${{ secrets.PRIVATE_KEY }}
 
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           ref: main
           fetch-depth: 0