E0368 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/issue-5239-1.rs

Error E0368 needs a span_label, updating it from:

error[E0368]: binary assignment operation `+=` cannot be applied to type `&isize`
  --> src/test/compile-fail/issue-5239-1.rs:14:39
   |
14 |     let x = |ref x: isize| -> isize { x += 1; };
   |                                       ^

To:

error[E0368]: binary assignment operation `+=` cannot be applied to type `&isize`
  --> src/test/compile-fail/issue-5239-1.rs:14:39
   |
14 |     let x = |ref x: isize| -> isize { x += 1; };
   |                                       ^ cannot use `+=` on `isize`

[leikahing]

I'll work on this.