Fix cx.windows() to return borrowed windows (#8086)

Fixes #8068

Release Notes:

- Fixed an error message when joining a project twice
([#8068](https://github.com/zed-industries/zed/issues/8068)).

crates/zed/src/zed.rs

@@ -422,8 +422,8 @@ fn quit(_: &Quit, cx: &mut AppContext) {
 
         // If multiple windows have unsaved changes, and need a save prompt,
         // prompt in the active window before switching to a different window.
-        cx.update(|cx| {
-            workspace_windows.sort_by_key(|window| window.is_active(&cx) == Some(false));
+        cx.update(|mut cx| {
+            workspace_windows.sort_by_key(|window| window.is_active(&mut cx) == Some(false));
         })
         .log_err();