Verified Commit d721ed18 authored by
gitlab-ci: Use versioned gcc:9 image for builds.
Use a versioned gcc container image as the base for more repeatable results. The version will need to be bumped periodically. Also reformat to follow current recommendations by moving the contianer image and tags under the `default` key. Signed-off-by: Marvin Scholz <firstname.lastname@example.org>