Fix clippy::uninlined_format_args warning

```
error: variables can be used directly in the `format!` string
  --> examples/print.rs:29:17
   |
29 |                 eprintln!("Received signal {:?}", signal);
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#uninlined_format_args
   = note: `-D clippy::uninlined-format-args` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::uninlined_format_args)]`
help: change this to
   |
29 -                 eprintln!("Received signal {:?}", signal);
29 +                 eprintln!("Received signal {signal:?}");
   |
```

Author: taiki-e

examples/print.rs

@@ -26,7 +26,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         signals
             .for_each(|signal| {
                 // Print the signal.
-                eprintln!("Received signal {:?}", signal);
+                eprintln!("Received signal {signal:?}");
 
                 // After printing it, do whatever the signal was supposed to do in the first place.
                 low_level::emulate_default_handler(signal.unwrap() as i32).unwrap();