gitlab-ci: run test suite in the buildserver environment
Run the whole test suite in an environment that is like the buildserver guest VM. This installs python3-babel because that is only used by the test suite, and not needed in the buildserver.
Some extra packages are required for this test run that are not provided by the buildserver since they are not needed there:
- gnupg-agent for the full signing setup
- python3-babel for compiling localization files
- python3-clint for fancy progress bars for users
https://gitlab.com/fdroid/ci-images-base is deprecated and archived.