Fix help message for modification to &T created by &{t}

[ibraheemdev]

Previous:

error[E0594]: cannot assign to `*x` which is behind a `&` reference
 --> src/main.rs:3:5
  |
2 |     let x: &usize = &mut{0};
  |                     ------- help: consider changing this to be a mutable reference: `&mut mut{0}`
3 |     *x = 1;
  |     ^^^^^^ `x` is a `&` reference, so the data it refers to cannot be written

[rust-highfive]

r? @oli-obk

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[oli-obk]

@bors r+ rollup

[bors]

📌 Commit b4a873f has been approved by oli-obk