PHP 8 tests (#5)

* added PHP-8 to test files

Author: pschocke

.github/workflows/php-cs-fixer.yml

@@ -9,7 +9,7 @@ jobs:
       fail-fast: true
       matrix:
         os: [ubuntu-latest, windows-latest]
-        php: [7.3, 7.4]
+        php: [7.3, 7.4, 8.0, 8.1, 8.2]
         dependency-version: [prefer-lowest, prefer-stable]
 
     name: P${{ matrix.php }} - ${{ matrix.dependency-version }} - ${{ matrix.os }}