Fix clippy::for_kv_map lint violations (#36493)

Release Notes:

- N/A

crates/gpui/src/platform/linux/wayland/client.rs

@@ -528,7 +528,7 @@ impl WaylandClient {
 
                             client.common.appearance = appearance;
 
-                            for (_, window) in &mut client.windows {
+                            for window in client.windows.values_mut() {
                                 window.set_appearance(appearance);
                             }
                         }

crates/gpui/src/platform/linux/x11/client.rs

@@ -456,7 +456,7 @@ impl X11Client {
                 move |event, _, client| match event {
                     XDPEvent::WindowAppearance(appearance) => {
                         client.with_common(|common| common.appearance = appearance);
-                        for (_, window) in &mut client.0.borrow_mut().windows {
+                        for window in client.0.borrow_mut().windows.values_mut() {
                             window.window.set_appearance(appearance);
                         }
                     }