Bump actions/checkout from 6 to 7

Bumps [actions/checkout](https://github.com/actions/checkout) from 6 to 7.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v6...v7)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '7'
  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

@@ -27,7 +27,7 @@ jobs:
           - { ruby: head, experimental: true }
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:

.github/workflows/isolated.yml

@@ -8,7 +8,7 @@ jobs:
         ruby: [2.7]
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
 
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1

.github/workflows/rubocop.yml

@@ -10,7 +10,7 @@ jobs:
         ruby: [2.7]
 
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
     - uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}