v9: Child templates is not nested under master on installation

[hjaltedaniel-umbraco]

Version of Umbraco: 9.0.0

When installing the starterkit from scratch on v9, the templates is not nested under the Master template.
That means that the UI for templates in the backoffice looks like this:

I'd expect them to look like this:

The templates themselves are fine - they have the correct Layout = "master.cshtml"; specified - so it looks to be an issue on the schema side of things.
I'd be happy to do a PR, but I'm not sure where the content lives in this package - if someone could point me in the right direction, I would be happy to do it 😅