Update use of actions/checkout to v4

examples/lumen-postgres.yml

@@ -39,7 +39,7 @@ jobs:
         php-versions: ['7.4', '8.0', '8.1']
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       # Docs: https://github.com/shivammathur/setup-php
       - name: Setup PHP