E0503 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/regions-escape-loop-via-vec.rs

E0503 needs a span_label and a span_note converted to a span_label, updating:

error[E0503]: cannot use `x` because it was mutably borrowed
  --> src/test/compile-fail/regions-escape-loop-via-vec.rs:16:13
   |
16 |         let mut z = x;
   |             ^^^^^
   |
note: borrow of `x` occurs here
  --> src/test/compile-fail/regions-escape-loop-via-vec.rs:14:28
   |
14 |     let mut _y = vec!(&mut x);
   |                            ^

To:

error[E0503]: cannot use `x` because it was mutably borrowed
  --> src/test/compile-fail/regions-escape-loop-via-vec.rs:16:13
   |
14 |    let mut _y = vec!(&mut x);
   |                           - mutably borrowed here
15 |    while x < 10 {
16 |         let mut z = x;
   |             ^^^^^ use of borrowed `x`

[wesleywiser]

I can take this