vlib/v/checker/tests/string_index_assign_error.vv:3:3: error: cannot assign to s[i] since V strings are immutable
(note, that variables may be mutable but string values are always immutable, like in Go and Java)
    1 | fn main() {
    2 |     mut a := 'V is great!!'
    3 |     a[0] = `R`
      |      ~~~
    4 | }
