use latest checkout action

Author: okaufmann

.github/workflows/run-tests.yml

@@ -39,7 +39,7 @@ jobs:
 
         steps:
             - name: Checkout code
-              uses: actions/checkout@v2
+              uses: actions/checkout@v3
 
             - name: Setup PHP
               uses: shivammathur/setup-php@v2