Update: use actions/checkout v4

Author: jordyvanderhaegen

.github/workflows/main.yml

@@ -37,7 +37,7 @@ jobs:
 
         steps:
             - name: Checkout code
-              uses: actions/checkout@v2
+              uses: actions/checkout@v4
 
             - name: Setup PHP
               uses: shivammathur/setup-php@v2