Update phpunit.yml

Author: casperbakker

.github/workflows/phpunit.yml

@@ -12,7 +12,7 @@ jobs:
 
     strategy:
       matrix:
-        php-versions: ['7.3', '7.4', '8.0', '8.1', '8.2']
+        php-versions: ['7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
 
     steps:
     - name: Checkout code