CI support stuff

Docker image

GitLab CI jobs run in a Docker image, defined here. To update that image (perhaps to install some more packages):

1. Edit .gitlab-ci/*.Dockerfile with the changes you want
2. Run .gitlab-ci/run-docker.sh build --base=debian-stable --base-version=1 to build the new image (bump the version from the latest listed for that base on https://gitlab.gnome.org/GNOME/glib/container_registry). If rebuilding the coverity.Dockerfile image, you’ll need to have access to Coverity Scan and will need to specify your project name and access token as the environment variables COVERITY_SCAN_PROJECT_NAME and COVERITY_SCAN_TOKEN.
3. Run .gitlab-ci/run-docker.sh push --base=debian-stable --base-version=1 to upload the new image to the GNOME GitLab Docker registry
   • If this is the first time you‘re doing this, you’ll need to log into the registry
   • If you use 2-factor authentication on your GNOME GitLab account, you'll need to create a personal access token and use that rather than your normal password — the token should have read_registry and write_registry permissions
4. Edit .gitlab-ci.yml (in the root of this repository) to use your new image