Bump actions/checkout from 3 to 4 (#519)

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
       matrix:
         ruby: ["2.3", "2.4", "2.5", "2.6", "2.7", "3.0", "3.1", "3.2", "head"]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -25,7 +25,7 @@ jobs:
       matrix:
         ruby: ["2.0", "2.1", "2.2"]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -49,7 +49,7 @@ jobs:
   rubocop:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -78,7 +78,7 @@ jobs:
             "head",
           ]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Cache Vagrant boxes
         uses: actions/cache@v3