Update .gitlab-ci.yml

1 job for wip/ci in 30 seconds
Name Stage Failure
validate Test
Checking out 03142fad as wip/ci...

Skipping Git submodules setup
Executing "step_script" stage of the job script
$ nix build
error: executing 'git': No such file or directory
error: program 'git' failed with exit code 1
(use '--show-trace' to show detailed location information)
ERROR: Job failed: exit code 1