vlib/v/checker/tests/immutable_struct_postfix.vv:8:2: error: `a` is immutable, declare it with `mut` to make it mutable
    6 | fn main() {
    7 |     a := Aaa{}
    8 |     a.i++
      |     ^
    9 |     a.i--
   10 | }
vlib/v/checker/tests/immutable_struct_postfix.vv:9:2: error: `a` is immutable, declare it with `mut` to make it mutable
    7 |     a := Aaa{}
    8 |     a.i++
    9 |     a.i--
      |     ^
   10 | }