Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/php.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Setup PHP with PECL extension
       uses: shivammathur/setup-php@v2