Bugfix: Correctly clear the urgency hint when the window is underneath a split-con (+test)

Previously, when you had an urgent container in a stack on some
invisible workspace (say urxvt) and you switched to it, the urgency hint
was not properly cleared.

src/workspace.c

@@ -322,6 +322,7 @@ static void workspace_defer_update_urgent_hint_cb(EV_P_ ev_timer *w, int revents
 
     DLOG("Resetting urgency flag of con %p by timer\n", con);
     con->urgent = false;
+    con_update_parents_urgency(con);
     workspace_update_urgent_flag(con_get_workspace(con));
     tree_render();