vlib/v/checker/tests/for_in_mut_string.vv:19:6: error: string type is immutable, it cannot be changed
   17 | 
   18 | fn wrap_text(mut gv Grid) {
   19 |     for mut ch in gv.header {
      |         ~~~
   20 |         println(ch)
   21 |     }
vlib/v/checker/tests/for_in_mut_string.vv:23:6: error: string type is immutable, it cannot be changed
   21 |     }
   22 | 
   23 |     for mut letter in 'abc' {
      |         ~~~
   24 |         bit := letter - 1
   25 |         println(bit)