Bump actions/checkout from 2 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v4)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/pr-check.yaml

@@ -8,7 +8,7 @@ jobs:
     name: Block fixup commits
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Block fixup commit merge
         uses: 13rac1/[email protected]

.github/workflows/tests.yaml

@@ -20,7 +20,7 @@ jobs:
     name: PHP ${{ matrix.php-version }} ${{ matrix.dependencies }}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
@@ -57,7 +57,7 @@ jobs:
       name: "Code style and static analysis"
       runs-on: ubuntu-latest
       steps:
-        - uses: actions/checkout@v2
+        - uses: actions/checkout@v4
 
         - name: Setup PHP
           uses: shivammathur/setup-php@v2
@@ -79,7 +79,7 @@ jobs:
     name: "Markdown link check"
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: gaurav-nelson/github-action-markdown-link-check@v1
         with:
           use-verbose-mode: 'yes'