Bump friendsofphp/php-cs-fixer in /composer/helpers

Bumps [friendsofphp/php-cs-fixer](https://github.com/FriendsOfPHP/PHP-CS-Fixer) from 2.16.7 to 2.16.8.
- [Release notes](https://github.com/FriendsOfPHP/PHP-CS-Fixer/releases)
- [Changelog](https://github.com/FriendsOfPHP/PHP-CS-Fixer/blob/2.16/CHANGELOG.md)
- [Commits](PHP-CS-Fixer/PHP-CS-Fixer@v2.16.7...v2.16.8)

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