ci: use php artisan test over phpunit command

[matthiasweiss]

This PR changes the test command from ./vendor/bin/phpunit to php artisan test.

EDIT: if this is wanted, I can also add a PR to the other starter kits

[tnylea]

Thanks, @matthiasweiss, I think we'll keep the ./vendor/bin/phpunit in the CI workflow just so that way it's clear which testing framework we are using, PHPUnit or PEST. In any other case, I would use php artisan test, but in this case, I think we'll keep that in there.