Updated Drupal to 8.6. This goes with the following updates because it's possible...

[yaffs-website] / vendor / symfony / dependency-injection / Tests / Fixtures / yaml / services_named_args.yml

services:
    Symfony\Component\DependencyInjection\Tests\Fixtures\NamedArgumentsDummy: { 0: ~, $apiKey: ABCD }

    another_one:
        class: Symfony\Component\DependencyInjection\Tests\Fixtures\NamedArgumentsDummy
        arguments:
            $apiKey: ABCD
            Symfony\Component\DependencyInjection\Tests\Fixtures\CaseSensitiveClass: ~
        calls:
            - ['setApiKey', { $apiKey: '123' }]