core/fix: stringify type in expected concrete type error

nac3core/src/typecheck/function_check.rs

@@ -80,7 +80,7 @@ impl<'a> Inferencer<'a> {
                 return Err(HashSet::from([format!(
                     "expected concrete type at {} but got {}",
                     expr.location,
-                    self.unifier.get_ty(*ty).get_type_name()
+                    self.unifier.stringify(*ty)
                 )]));
             }
         }