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

@@ -35,7 +35,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
@@ -72,7 +72,7 @@ jobs:
         cd /tmp
         mv -v html html.pr
     - name: Checkout base
-      uses: actions/checkout@v6
+      uses: actions/checkout@v7
       with:
         ref: ${{ github.event.pull_request.base.sha }}
     - name: Install dependencies (base)
@@ -98,7 +98,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
     - name: Install misspell
       run: 'curl -L https://git.io/misspell | bash'
     - name: Run misspell