Review app (dynamic environment) created from child pipeline does not show up in merge requests.

Summary

Set dynamic environment from a child pipeline does not create review app links in merge request.

Steps to reproduce

Parent pipeline

stages:
    - trigger
    
trigger-job:
    stage: trigger
    trigger:
        include: child.yml
        strategy: depend

Child pipeline

stages:
    - deploy

deploy_review:
    stage: deploy
    script:
        - echo "Deploy a review app"
    environment:
        name: foo/$CI_COMMIT_REF_NAME
        url: https://$CI_ENVIRONMENT_SLUG.example.com
    only:
        - branches
    except:
        - master 

deploy_review2:
    stage: deploy
    script:
        - echo "Deploy a review app"
    environment:
        name: foo2/$CI_COMMIT_REF_NAME
        url: https://url.$CI_ENVIRONMENT_SLUG.example.com
    only:
        - branches
    except:
        - master 

Preview link does not show up in the merge request.

Example Project

TBD

What is the current bug behavior?

review app button does not show up when dynamic environments were created in child pipeline

What is the expected correct behavior?

review app button shows up when dynamic environments were created in child pipeline.

I think it's acceptable to not display placeholder as child pipeline may create dynamically. but when child pipeline completed review app button should be displayed.

Relevant logs and/or screenshots

No review app button is created for the example pipeline configuration.

Output of checks

(If you are reporting a bug on GitLab.com, write: This bug happens on GitLab.com)

Results of GitLab environment info

GitLab Enterprise Edition 12.10.3-ee