error: invalid key type `Newtype6`
   ╭▸ test/ui/invalid_key_type.aldrin:37:21
   │
37 │ newtype Set12 = set<Newtype6>;
   │                     ━━━━━━━━ type used here
   │
   ├ help: allowed key types are `u8`, `i8`, `u16`, `i16`, `u32`, `i32`, `u64`, `i64`,
   │       `string`, `uuid` and newtypes resolving to one of those
   ╰ note: `Newtype6` is a newtype, that resolves to `unit`