Fix environment variable access for OPENAI_DEFAULT_MODEL

Author: guylei-code

modules/src/openai_proxy_app/openai_proxy_app.ipynb

@@ -62,7 +62,7 @@
     "project.set_secrets({\n",
     "    \"OPENAI_BASE_URL\": os.environ[\"OPENAI_BASE_URL\"],\n",
     "    \"OPENAI_API_KEY\": os.environ[\"OPENAI_API_KEY\"],\n",
-    "    \"OPENAI_DEFAULT_MODEL\": os.getenv(\"OPENAI_DEFAULT_MODEL\", \"gpt-4o-mini\")\n",
+    "    \"OPENAI_DEFAULT_MODEL\": os.environ(\"OPENAI_DEFAULT_MODEL\", \"gpt-4o-mini\")\n",
     "})"
    ],
    "id": "5f7e307b080860a2"