Gitlab update - CI future proofing required

Hi all,

Over this weekend I completed a series of updates to invent.kde.org, moving
it to the latest supported version of Postgres (14) and Gitlab (16.6).

As part of that Gitlab update, additional security policies began to be
enforced by Gitlab which mean our existing method of including CI templates
is now beginning to be problematic.

To correct this, we need to port our .gitlab-ci.yml files over to the
include:project syntax (see
https://docs.gitlab.com/ee/ci/yaml/#includeproject)

As an example, this might look like for a Qt 6 only project with Linux,
FreeBSD and Windows builds:

include:
  - project: sysadmin/ci-utilities
    file:
      - /gitlab-templates/linux-qt6.yml
      - /gitlab-templates/freebsd-qt6.yml
      - /gitlab-templates/windows-qt6.yml

While we've been able to permit the existing syntax to work for now, it is
recommended that projects please look into porting their CI configurations
now to avoid future issues.

Thanks,
Ben