Bump actions/checkout from 5.0.1 to 6.0.0

Bumps [actions/checkout](https://github.com/actions/checkout) from 5.0.1 to 6.0.0.
- [Release notes](https://github.com/actions/checkout/releases)
- [Commits](actions/checkout@v5.0.1...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: 6.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -39,7 +39,7 @@ jobs:
         - { os: windows-latest, ruby: head }
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v6.0.0
 
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1

.github/workflows/push_gem.yml

@@ -31,7 +31,7 @@ jobs:
         with:
           egress-policy: audit
 
-      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5.0.1
+      - uses: actions/checkout@c2d88d3ecc89a9ef08eebf45d9637801dcee7eb5 # v5.0.1
 
       - name: Set up Ruby
         uses: ruby/setup-ruby@d5126b9b3579e429dd52e51e68624dda2e05be25 # v1.267.0

.github/workflows/sync-ruby.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     if: ${{ github.repository_owner == 'ruby' }}
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v6.0.0
 
       - name: Create GitHub App token
         id: app-token