config.toml - environment NOT read

Summary

When I have set this in either /etc/gitlab-runner/config.toml or ~/.gitlab-runner/config.toml:

[[runners]]
  environment = ["CI_BUILD_REF_NAME=snapshot"]

and then run a pipeline locally using: gitlab-runner exec docker test-pre

My job fails - as CI_BUILD_REF_NAME isn't set.

Docs says it reads config.toml - so that environment variable should be set AFAIK.