Gitlab-runner on k8s : x509: certificate signed by unknown authority

Can't add gitlab runner through Admin Area >> Kubernetes Clusters >> Cluster_NAME >> Applications >> Gitlab Runner Install.

Gitlab said the runner was successfully installed but in the pod logs I receive the following error message:

runner=iQgEyY37 status=couldn't execute POST against https://server_name.my.domain/api/v4/jobs/request: Post https://server_name.my.domain/api/v4/jobs/request: x509: certificate signed by unknown authority

I'm not using a self-signed certificate. The certificate is from GlobalSign nv-sa. Where can I config a certificate for this type of gitlab runner installation?

Helm: 2.16.9

Gitlab: 13.1.1

K8s: 1.8.6