Try to implement zombie spawning

src/Game.cpp

@@ -18,6 +18,8 @@ void Game::update(std::stop_token stop_token)
     while (!stop_token.stop_requested()) {
         game_mutex.lock();
 
+        ticks++;
+
         player.update();
 
         for (Arrow *arrow : arrows) {
@@ -25,7 +27,11 @@ void Game::update(std::stop_token stop_token)
         }
 
         for (Zombo *zombo : zombos) {
-            zombo->update(player.x, player.y); // doesn't work :((((
+            zombo->update(player.x, player.y);
+        }
+
+        if (ticks % 1000 == 0) {
+            zombos.push_back(new Zombo(&renderer, 20.0, 20.0));  // doesn't work :((((
         }
 
         renderer.redraw();