Difficulty adding a parent menu link
Instead of using route_name: &lt;nolink&gt;, I suggest providing a route for the link and e.g. pointing that route to Drupal's default overview page contoller. This should fix your issue and assures the users can click the menu link and get an overview of the available functions (e.g. when re-using your module in a Drupal that has no Admin Toolbar installed):

mymodule.links.menu.yml

scrape.migration:
  title: 'Migration'
  description: 'Migration functions'
  parent: system.admin_config_development
  route_name: scrape.migration


mymodule.routing.yml

scrape.migration:
  path: '/admin/config/development/scrape'
  defaults:
    _controller: '\Drupal\system\Controller\SystemController::overview'
    link_id: 'scrape.migration'
    _title: 'Migration'
  requirements:
    _permission: 'access administration pages'


You might have to adapt the path/permissions accordingly.