chore: Fix violations of elided_named_lifetimes (#18330)

I compile Zed from nightly build pretty often and I've noticed that
we're getting a few hits on new rustc lint:
https://github.com/rust-lang/rust/pull/129207

Release Notes:

- N/A

crates/sum_tree/src/tree_map.rs

@@ -105,7 +105,7 @@ impl<K: Clone + Ord, V: Clone> TreeMap<K, V> {
         cursor.item().map(|item| (&item.key, &item.value))
     }
 
-    pub fn iter_from<'a>(&'a self, from: &'a K) -> impl Iterator<Item = (&K, &V)> + '_ {
+    pub fn iter_from<'a>(&'a self, from: &'a K) -> impl Iterator<Item = (&'a K, &'a V)> + 'a {
         let mut cursor = self.0.cursor::<MapKeyRef<'_, K>>(&());
         let from_key = MapKeyRef(Some(from));
         cursor.seek(&from_key, Bias::Left, &());