Some pages in the docs don't appear in the side navigation

[rw251]

Namely the schema docs:

• https://docs.opensafely.org/ehrql/reference/schemas/tpp/
• https://docs.opensafely.org/ehrql/reference/schemas/core/
• https://docs.opensafely.org/ehrql/reference/schemas/emis/
• https://docs.opensafely.org/ehrql/reference/schemas/raw.tpp/
• https://docs.opensafely.org/ehrql/reference/schemas/raw.core/
• https://docs.opensafely.org/ehrql/reference/schemas/raw.emis/

I don't know enough about mkdocs to know if this is an issue with the ehrql docs, or the opensafely documentation wrapper.