### What?
Turborepo fails to compile due to type error in the generated drizzle
schema.
### Why?
TypeScript may not include the module augmentation for
@payloadcms/db-postgres, especially in monorepo or isolated module
builds. This causes type errors during the compilation process of
turborepo project. Adding the type-only import guarantees that
TypeScript loads the relevant type definitions and augmentations,
resolving these errors.
### How?
This PR adds a type-only import statement to ensure TypeScript
recognizes the module augmentation for @payloadcms/db-postgres in the
generated drizzle schema from payload, and there is no runtime effect.
Fixes#12311
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