Downstream Git/Composer Issues
Roundearth just recently switched to using civicrm-asset-plugin and it may not be fully integrated yet.

CiviCRM can be installed on drupal 8 without roundearth now - it's still not "official" but is being used by some.

composer create-project drupal/recommended-project some-folder

cd some-folder

# replace the 'x' below with a proper version number

composer require civicrm/civicrm-core:5.x.x civicrm/civicrm-packages:5.x.x civicrm/civicrm-drupal-8:5.x.x civicrm/civicrm-asset-plugin:~1.0.1 

Install Drupal as usual

Then to install CiviCRM - make sure the civicrm.settings.php file can be created -> by making the web/sites/default directory writeable:

chmod +w web/sites/default

Then you can either go to Extend and enable CiviCRM Core
or you can do this from the command line:

drush en -y civicrm