docs: add missing api key to cross-thread persistence howto (#3141)

docs/docs/how-tos/cross-thread-persistence.ipynb

@@ -64,18 +64,10 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": null,
    "id": "aa2c64a7",
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "ANTHROPIC_API_KEY:  ········\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "import getpass\n",
     "import os\n",
@@ -86,7 +78,8 @@
     "        os.environ[var] = getpass.getpass(f\"{var}: \")\n",
     "\n",
     "\n",
-    "_set_env(\"ANTHROPIC_API_KEY\")"
+    "_set_env(\"ANTHROPIC_API_KEY\")\n",
+    "_set_env(\"OPENAI_API_KEY\")"
    ]
   },
   {
@@ -356,7 +349,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.11.9"
+   "version": "3.12.3"
   }
  },
  "nbformat": 4,