chore: Fix warnings for Rust 1.89 (#32378)

Closes #ISSUE

Release Notes:

- N/A

crates/sum_tree/src/sum_tree.rs

@@ -380,7 +380,7 @@ impl<T: Item> SumTree<T> {
         items
     }
 
-    pub fn iter(&self) -> Iter<T> {
+    pub fn iter(&self) -> Iter<'_, T> {
         Iter::new(self)
     }