Required : Pipelines should only trigger in creation of merge_requests not on updation of merge_requests

GitLab CI/CD
1

Required : Pipelines should only trigger in creation of merge_requests not on updation of merge_requests. But not happening with below rule

rules:
- if: $CI_PIPELINE_SOURCE == “push”
when: never
- if: $CI_PIPELINE_SOURCE == “merge_request_event”

What else should i add in it ?

Thanks