Merge rust-bitcoin#4285: chore: remove explicit into iteration

e966335 chore: remove explicit into iteration (jike)

Pull request description:

  ```
  warning: it is more concise to loop over containers instead of using explicit iteration methods
     --> bitcoin/src/psbt/serialize.rs:209:21
      |
  209 |         for cnum in self.1.into_iter() {
      |                     ^^^^^^^^^^^^^^^^^^ help: to write this more concisely, try: `&self.1`
  ```

ACKs for top commit:
  Kixunil:
    ACK e966335
  apoelstra:
    ACK e966335; successfully ran local tests

Tree-SHA512: 32fced1a5aba2caa6e48a2e586bf00dcf3d4b82b6b530d9c7f535b530737a40e24d5c05a7cea40747df4c7c4698ec141683b9416583b185b1ff6461f3c8f667f

Author: apoelstra

bitcoin/src/psbt/serialize.rs

@@ -206,7 +206,7 @@ impl Serialize for KeySource {
 
         rv.append(&mut self.0.to_byte_array().to_vec());
 
-        for cnum in self.1.into_iter() {
+        for cnum in &self.1 {
             rv.append(&mut serialize(&u32::from(*cnum)))
         }