update checkout GitHub action to version 4

Author: xabbuh

.github/workflows/ci.yaml

@@ -17,7 +17,7 @@ jobs:
 
     steps:
       - name: 'Check out'
-        uses: 'actions/checkout@v2'
+        uses: 'actions/checkout@v4'
 
       - name: 'Set up PHP'
         uses: 'shivammathur/setup-php@v2'
@@ -42,7 +42,7 @@ jobs:
 
     steps:
       - name: 'Check out'
-        uses: 'actions/checkout@v2'
+        uses: 'actions/checkout@v4'
 
       - name: 'Set up PHP'
         uses: 'shivammathur/setup-php@v2'