Gitlab-runner, docker-machine executor -> how to pass cacert to docker-machine?

Can anyone tell me how to pass cacert to created docker-machine?
I have custom certs on gitlab-ci instance.
Problem:
I am registering gitlab-runner on foo_server, its is working, (with --tls-ca-file=/etc/gitlab-runner/certs/ca.crt)… I am seeing that foo_runner_server is created in cloud, problem is when it tries to clone git repo.

fatal: unable to access ‘https://gitlab-ci-token:xxxxxxxxxxxxxxxxxxxx@mydomain.com/root/hello-world.git/’: SSL certificate problem: unable to get issuer certificate

So my question is how to pass cacert to docker-machine server to container to be able to clone from git

Thanks

EDIT: I guess that /etc/gitlab-runner/certs/ca.crt from gitlab-runner is transfered via docker-machine to target host and then is used some kind of magic, like mount volume to build container, or content is loaded to ENV variable and then its used in build container ? …
Of course, its is working with --env=“GIT_SSL_NO_VERIFY=true”