Fix clippy::for_kv_map lint violations (#36493)

Release Notes:

- N/A

crates/agent_ui/src/agent_diff.rs

@@ -1643,7 +1643,7 @@ impl AgentDiff {
                 continue;
             };
 
-            for (weak_editor, _) in buffer_editors {
+            for weak_editor in buffer_editors.keys() {
                 let Some(editor) = weak_editor.upgrade() else {
                     continue;
                 };