Github Actions: Upgrade checkout action to v3

Author: Naktibalda

.github/workflows/main.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: 'ubuntu-latest'
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Install PHP
         uses: shivammathur/setup-php@v2
@@ -34,7 +34,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
 
     - name: Setup PHP
       uses: shivammathur/setup-php@v2