Tweak `&mut self` suggestion span

```
error[E0596]: cannot borrow `*self.s` as mutable, as it is behind a `&` reference
  --> $DIR/issue-38147-1.rs:17:9
   |
LL |         self.s.push('x');
   |         ^^^^^^ `self` is a `&` reference, so the data it refers to cannot be borrowed as mutable
   |
help: consider changing this to be a mutable reference
   |
LL |     fn f(&mut self) {
   |           +++
```

Note the suggestion to add `mut` instead of replacing the entire `&self` with `&mut self`.

…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#133382 (Suggest considering casting fn item as fn pointer in more cases)
 - rust-lang#136092 (Test pipes also when not running on Windows and Linux simultaneously)
 - rust-lang#136190 (Remove duplicated code in RISC-V asm bad-reg test)
 - rust-lang#136192 (ci: remove unused windows runner)
 - rust-lang#136205 (Properly check that array length is valid type during built-in unsizing in index)
 - rust-lang#136211 (Update mdbook to 0.4.44)
 - rust-lang#136212 (Tweak `&mut self` suggestion span)
 - rust-lang#136214 (Make crate AST mutation accessible for driver callback)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#136212 - estebank:span-tweak, r=petrochenkov

Tweak `&mut self` suggestion span

```
error[E0596]: cannot borrow `*self.s` as mutable, as it is behind a `&` reference
  --> $DIR/issue-38147-1.rs:17:9
   |
LL |         self.s.push('x');
   |         ^^^^^^ `self` is a `&` reference, so the data it refers to cannot be borrowed as mutable
   |
help: consider changing this to be a mutable reference
   |
LL |     fn f(&mut self) {
   |           +++
```

Note the suggestion to add `mut` instead of replacing the entire `&self` with `&mut self`.

…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#133382 (Suggest considering casting fn item as fn pointer in more cases)
 - rust-lang#136092 (Test pipes also when not running on Windows and Linux simultaneously)
 - rust-lang#136190 (Remove duplicated code in RISC-V asm bad-reg test)
 - rust-lang#136192 (ci: remove unused windows runner)
 - rust-lang#136205 (Properly check that array length is valid type during built-in unsizing in index)
 - rust-lang#136211 (Update mdbook to 0.4.44)
 - rust-lang#136212 (Tweak `&mut self` suggestion span)
 - rust-lang#136214 (Make crate AST mutation accessible for driver callback)

r? `@ghost`
`@rustbot` modify labels: rollup