Update listdir() in sample code to take correct args (#2261)

Executing this code (Python 3.11, MacOS) returns error
`TypeError: listdir: path should be string, bytes, os.PathLike, integer or None, not TemporaryDirectory`
Using the string name of the dir works better.

website/docs/tutorial/code-executors.ipynb

@@ -198,7 +198,7 @@
    "source": [
     "import os\n",
     "\n",
-    "print(os.listdir(temp_dir))\n",
+    "print(os.listdir(temp_dir.name))\n",
     "# We can see the output scatter.png and the code file generated by the agent."
    ]
   },