Split/auto publish

LMS-11017 https://openedx.atlassian.net/browse/LMS-11017
Isn't this False b/c `sequential` is direct only rather than b/c of what you're trying to test?

I'm not following why this test is legitimate. Do we really want the ability for xblocks to point to non-existent children? I know old mongo did this in order for direct only leaves to point to private children, but that was a defect of that modulestore not something we want to impose on other stores. It had no user visible value and just polluted the logs with lots of ItemNotFoundError(s).