GH Actions: use PHP Parallel Lint
GH Actions: use PHP Parallel Lint

... for faster linting results.

Ref: https://github.com/php-parallel-lint/PHP-Parallel-Lint/

The results of PHP Parallel Lint can also be used in combination with [cs2pr](https://github.com/staabm/annotate-pull-request-from-checkstyle) to show any issues in-line in the GH (PR) code view.

Brain-WP/BrainMonkey