windowPreview: Don't hide overlay while hovering icon

We should treat the icon like we do the caption or close button,
and still consider the preview hovered when the pointer is over
the icon.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3049>

js/ui/windowPreview.js

@@ -577,6 +577,7 @@ export const WindowPreview = GObject.registerClass({
             GLib.PRIORITY_DEFAULT,
             WINDOW_OVERLAY_IDLE_HIDE_TIMEOUT, () => {
                 if (this._closeButton['has-pointer'] ||
+                    this._icon['has-pointer'] ||
                     this._title['has-pointer'])
                     return GLib.SOURCE_CONTINUE;