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/check_changelog.yml

@@ -13,7 +13,7 @@ jobs:
       !contains(github.event.pull_request.body, '[skip ci]') &&
       !contains(github.event.pull_request.labels.*.name, 'skip changelog')
     steps:
-      - uses: actions/checkout@v5.0.0
+      - uses: actions/checkout@v6
       - name: Check that CHANGELOG is touched
         run: |
           git fetch origin ${{ github.base_ref }} --depth 1 && \

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5.0.0
+        uses: actions/checkout@v6
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -34,7 +34,7 @@ jobs:
         ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5.0.0
+        uses: actions/checkout@v6
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -53,7 +53,7 @@ jobs:
         ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5.0.0
+        uses: actions/checkout@v6
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:

.github/workflows/sync-ruby.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     if: ${{ github.repository_owner == 'ruby' }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Create GitHub App token
         id: app-token