docs: Fix Visualization Tutorial (main branch) (#2271)

The scheduler was removed from the example model used, so the docs started failing.

docs/tutorials/visualization_tutorial.ipynb

@@ -208,7 +208,7 @@
     "    # plt.figure(), for thread safety purpose\n",
     "    fig = Figure()\n",
     "    ax = fig.subplots()\n",
-    "    wealth_vals = [agent.wealth for agent in model.schedule.agents]\n",
+    "    wealth_vals = [agent.wealth for agent in model.agents]\n",
     "    # Note: you have to use Matplotlib's OOP API instead of plt.hist\n",
     "    # because plt.hist is not thread-safe.\n",
     "    ax.hist(wealth_vals, bins=10)\n",