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

[yaffs-website] / web / core / modules / system / tests / modules / system_incompatible_core_version_dependencies_test / system_incompatible_core_version_dependencies_test.info.yml

name: 'System incompatible core version dependencies test'
type: module
description: 'Support module for testing system dependencies.'
package: Testing
version: VERSION
core: 8.x
dependencies:
  - drupal:system_incompatible_core_version_test