Function revocation_backend_is_postgres 

pub fn revocation_backend_is_postgres(schema: &CompiledSchema) -> bool

Returns true when token revocation is enabled with the postgres backend.

Non-PostgreSQL runtime paths use this to warn that the backend is unavailable: the binary cannot connect a PostgreSQL pool from, e.g., a MySQL database_url, so revocation_manager_from_schema defers the backend and nothing builds it.