tests: remove phpcs-fixer --diff-fomat option

the option `--diff-format` no longer exist see also
PHP-CS-Fixer/PHP-CS-Fixer#3384

Author: gimler

.github/workflows/static.yml

@@ -11,7 +11,7 @@ jobs:
       - name: PHP-CS-Fixer
         uses: docker://jakzal/phpqa:php7.3-alpine
         with:
-            args: php-cs-fixer fix --dry-run --diff-format udiff -vvv
+            args: php-cs-fixer fix --diff --dry-run -vvv
 
   phpstan:
     name: PHPStan