QA: Update GHA workflow to run tests on PHP 8.3 (#89)

Author: michalbundyra

.github/workflows/phpunit.yml

@@ -11,7 +11,7 @@ jobs:
       max-parallel: 15
       matrix:
         operating-system: [macOS-latest, ubuntu-latest, windows-latest]
-        php-versions: ['8.0', '8.1', '8.2']
+        php-versions: ['8.0', '8.1', '8.2', '8.3']
     name: PHP ${{ matrix.php-versions }} on ${{ matrix.operating-system }}
     steps:
       - name: Checkout