Update: use checkout@v4 in workflows

Author: jordyvanderhaegen

.github/workflows/main.yml

@@ -35,7 +35,7 @@ jobs:
 
         steps:
             - name: Checkout code
-              uses: actions/checkout@v2
+              uses: actions/checkout@v4
 
             - name: Setup PHP
               uses: shivammathur/setup-php@v2