Update actions/checkout action to v6 (#272)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/test.yml

@@ -21,7 +21,7 @@ jobs:
           - php-version: '8.4'
             composer-flags: '--prefer-lowest'
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
@@ -42,7 +42,7 @@ jobs:
     name: PHP 8.4 - Test with coverage
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
@@ -69,7 +69,7 @@ jobs:
     name: PHP quality checks
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
@@ -87,7 +87,7 @@ jobs:
     name: Typescript quality checks
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Use Node.js 22.x
         uses: actions/setup-node@v6
@@ -111,7 +111,7 @@ jobs:
       contents: write
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           ref: ${{ github.head_ref }}