Bump actions/checkout from 3 to 4 (#9)

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] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yaml

@@ -19,7 +19,7 @@ jobs:
           - "8.1"
 
     steps:
-      - uses: "actions/checkout@v3"
+      - uses: "actions/checkout@v4"
       - uses: "shivammathur/setup-php@v2"
         with:
           coverage: "none"
@@ -47,7 +47,7 @@ jobs:
             code-coverage: "pcov"
 
     steps:
-      - uses: "actions/checkout@v3"
+      - uses: "actions/checkout@v4"
       - uses: "shivammathur/setup-php@v2"
         with:
           coverage: "${{ matrix.code-coverage }}"
@@ -80,7 +80,7 @@ jobs:
           - "8.1"
 
     steps:
-      - uses: "actions/checkout@v3"
+      - uses: "actions/checkout@v4"
       - uses: "shivammathur/setup-php@v2"
         with:
           coverage: "none"