use latest checkout also for phpstan

Author: dbu

.github/workflows/coding-standards.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v3"
+        uses: "actions/checkout@v4"
       - name: PHPStan
         uses: "docker://oskarstark/phpstan-ga"
         env: