seat/keyboard: constify wlr_seat_keyboard_send_modifiers()

include/wlr/types/wlr_seat.h

@@ -510,7 +510,7 @@ void wlr_seat_keyboard_send_key(struct wlr_seat *seat, uint32_t time_msec,
  * wlr_seat_keyboard_notify_modifiers() instead.
  */
 void wlr_seat_keyboard_send_modifiers(struct wlr_seat *seat,
-		struct wlr_keyboard_modifiers *modifiers);
+		const struct wlr_keyboard_modifiers *modifiers);
 
 /**
  * Send a keyboard enter event to the given surface and consider it to be the

types/seat/wlr_seat_keyboard.c

@@ -192,7 +192,7 @@ static void seat_keyboard_handle_surface_destroy(struct wl_listener *listener,
 }
 
 void wlr_seat_keyboard_send_modifiers(struct wlr_seat *seat,
-		struct wlr_keyboard_modifiers *modifiers) {
+		const struct wlr_keyboard_modifiers *modifiers) {
 	struct wlr_seat_client *client = seat->keyboard_state.focused_client;
 	if (client == NULL) {
 		return;