vlib/v/checker/tests/assign_expr_type_err_e.vv:3:2: error: operator `-=` not defined on left operand type `string`
    1 | fn main() {
    2 |     mut foo := 'hello'
    3 |     foo -= `a`
      |     ~~~
    4 |     _ = foo
    5 | }
vlib/v/checker/tests/assign_expr_type_err_e.vv:3:9: error: invalid right operand: string -= rune
    1 | fn main() {
    2 |     mut foo := 'hello'
    3 |     foo -= `a`
      |            ~~~
    4 |     _ = foo
    5 | }
vlib/v/checker/tests/assign_expr_type_err_e.vv:3:9: error: cannot assign to `foo`: expected `string`, not `rune`
    1 | fn main() {
    2 |     mut foo := 'hello'
    3 |     foo -= `a`
      |            ~~~
    4 |     _ = foo
    5 | }
