fix: generate pointer types for nullable enum columns with emit_pointers_for_null_types

[stampflit]

fixes https://github.com/sqlc-dev/sqlc/issues/4052

The generated QueryParams struct for the example from the issue is indeed:

type SearchFoodParams struct {
    Food     string
    FoodType *FoodType
}

I wrote a minimal example to verify that this works as intended with sqlc.

[stampflit]

Bump