Update GitHub Actions to use actions/checkout@v3

Author: ewilan-riviere

.github/workflows/phpstan-php-code.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v3
       - uses: php-actions/composer@v6
       - uses: php-actions/phpstan@v3
         with: