[PHPStan] Fix PHPStan notice on ParallelFileProcessor

[samsonasik]

Tried locally, PHPStan got notice:

composer phpstan         
> php -dmemory_limit=1G vendor/bin/phpstan analyse --ansi --error-format symplify
Note: Using configuration file /Users/samsonasik/www/rector-src/phpstan.neon.
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  packages/Parallel/Application/ParallelFileProcessor.php:59
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  - '#Instead of array shape, use value object with specific types in constructor and getters#'
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 [ERROR] Found 1 errors           

This PR ignored it in phpstan.neon