Add job to trigger GitLab mirror

Niklas van Schrickrequested to merge
trigger-gitlab-mirror-automatically into main

The GitLab mirror is really often not updating for more than 5 hours.

You can see at https://gitlab.com/gitlab-community/meta/-/work_items?sort=created_date&state=all&label_name%5B%5D=mirror-failure&first_page_size=20 that this is happening multiple times a day.

To prevent that, we will create a schedule to trigger the mirror manually.

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