editor: Correct "Toggle Excerpt Fold" tip on macOS (#38487)

Show `"Option+click to toggle all"` instead of `"Alt+click to toggle
all" on macOS.

<img width="546" height="212" alt="Screenshot 2025-09-19 at 10 16 11"
src="https://github.com/user-attachments/assets/b1052b7c-349f-4a11-892b-988cfd2ff365"
/>

Release Notes:

- N/A

crates/editor/src/element.rs

@@ -3838,7 +3838,11 @@ impl EditorElement {
                                                 Tooltip::with_meta_in(
                                                     "Toggle Excerpt Fold",
                                                     Some(&ToggleFold),
-                                                    "Alt+click to toggle all",
+                                                    if cfg!(target_os = "macos") {
+                                                        "Option+click to toggle all"
+                                                    } else {
+                                                        "Alt+click to toggle all"
+                                                    },
                                                     &focus_handle,
                                                     window,
                                                     cx,