Ignore clippy::infallible_destructuring_match lint

```
error: you seem to be trying to use `match` to destructure a single infallible pattern. Consider using `let`
  --> src/reaper/wait.rs:71:13
   |
71 | /             let inner = match &mut child.inner {
72 | |                 super::ChildGuard::Wait(inner) => inner,
73 | |                 #[cfg(not(windows))]
74 | |                 _ => unreachable!(),
75 | |             };
   | |______________^ help: try: `let super::ChildGuard::Wait(inner) = &mut child.inner;`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#infallible_destructuring_match
   = note: `-D clippy::infallible-destructuring-match` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::infallible_destructuring_match)]`
```

Author: taiki-e

src/reaper/wait.rs

@@ -68,6 +68,7 @@ impl Reaper {
             let mut child = child.lock().unwrap();
 
             // Get the inner child value.
+            #[allow(clippy::infallible_destructuring_match)] // false positive: should respect cfg
             let inner = match &mut child.inner {
                 super::ChildGuard::Wait(inner) => inner,
                 #[cfg(not(windows))]