Modify CI workflow for PHP code style checks

Run PHP-CS Fixer only for lowest supported PHP Version as recommended by php-cs-fixer

Author: samuelwei

.github/workflows/ci.yml

@@ -52,8 +52,8 @@ jobs:
       run: composer install --dev --no-interaction
       continue-on-error: ${{ matrix.experimental }}
     - name: Execute code style check via php-cs-fixer
+      if: ${{ matrix.php-versions == '8.1' }}
       run: tools/php-cs-fixer fix --dry-run
-      continue-on-error: ${{ matrix.experimental }}
     - name: Execute tests with coverage
       if: ${{ !matrix.experimental }}
       run: |