error: invalid key type `Newtype2`
   ╭▸ test/ui/invalid_key_type.aldrin:33:20
   │
33 │ newtype Set8 = set<Newtype2>;
   │                    ━━━━━━━━ 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: `Newtype2` is a newtype, that resolves to `unit`