Use images from the GitLab Docker registry

Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>

.gitlab-ci.yml

-image: docker-registry.apertis.org/apertis/apertis-v2020pre-testcases-builder
+image: registry.gitlab.apertis.org/infrastructure/apertis-docker-images/v2021dev1-testcases-builder
 
 test-renderer:
   stage: test