Bump actions/checkout from 3 to 4 (#22)

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/phpstan.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
 
     - name: Setup PHP
       uses: shivammathur/setup-php@v2

.github/workflows/tests.yml

@@ -14,7 +14,7 @@ jobs:
 
         steps:
             - name: Checkout code
-              uses: actions/checkout@v3
+              uses: actions/checkout@v4
 
             - name: Setup PHP
               uses: shivammathur/setup-php@v2