server: check backend support for timelines

References: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/4848

sway/server.c

@@ -251,7 +251,8 @@ bool server_init(struct sway_server *server) {
 		}
 	}
 	if (wlr_renderer_get_drm_fd(server->renderer) >= 0 &&
-			server->renderer->features.timeline) {
+			server->renderer->features.timeline &&
+			server->backend->features.timeline) {
 		wlr_linux_drm_syncobj_manager_v1_create(server->wl_display, 1,
 			wlr_renderer_get_drm_fd(server->renderer));
 	}