Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/quality-assurance.yml

@@ -16,7 +16,7 @@ jobs:
       matrix:
         php-version: [8.3]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php-version }}
@@ -29,7 +29,7 @@ jobs:
       matrix:
         php-version: [8.3, 8.4]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php-version }}