Bump actions/checkout from 3 to 4 (#55)

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>

Author: dependabot[bot]

.github/workflows/php-cs-fixer.yml

@@ -8,7 +8,7 @@ jobs:
 
         steps:
             - name: Checkout code
-              uses: actions/checkout@v3
+              uses: actions/checkout@v4
 
             - name: Run PHP CS Fixer
               uses: docker://oskarstark/php-cs-fixer-ga

.github/workflows/run-tests.yml

@@ -20,7 +20,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Cache dependencies
         uses: actions/cache@v3