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

[yaffs-website] / web / core / modules / menu_link_content / tests / menu_link_content_dynamic_route / menu_link_content_dynamic_route.info.yml

name: 'Menu link content dynamic route'
type: module
core: 8.x
hidden: true
dependencies:
  - drupal:menu_link_content