Retry child pipelines

Current gitlab version (12.8.1, selfhosted) rejects a build step containing a child-pipeline trigger when it contains a retry keyword.

example being rejected by yaml validation:

test_step:
    stage: test
    retry: 1
    trigger:
        include:
            - local: .gitlab-ci_child.yml
        strategy: depend

fails with
jobs:test_step config contains unknown keys: retry

Is this expected behavior?

I would love to bundle two sequential build steps into a single retry mechanic. (for me the steps are starting a specific parallels/virtualbox vm on the host machine and running the second step inside that machine once it becomes available. The first step here is sometimes brittle depending on host system state, so worth retrying)