How do add a missing config attribute to the gitlab-runner service

Does anyone know how I could modify the services.gitlab-runner such that I can add some more configuration to the gitlab-runner’s config.toml.

There are lots of variables but specifically, I’m trying to add allowed_pull_policies.

For some reason, I can’t find the config.toml that the NixOS gitlab-runner is using so it’s tough to even guess and check. gitlab-runner list says that it’s at /etc/gitlab-runner/config.toml but there’s no file there so I’m assuming that’s just hardcoded somewhere.

There is a services.gitlab-runner.settings option but it seems to completely overwrite the generated config.toml… so it sort of renders the other options of passing in secrets unusable.
Thanks.