error: invalid key type `unit`
   ╭▸ test/ui/invalid_key_type.aldrin:27:20
   │
27 │ newtype Set2 = set<unit>;
   │                    ━━━━ 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