docs: Update why.ipynb (#19173)

I think that cell type for pip command may be 'code'.
Please check, thank you :)

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, hwchase17.

docs/docs/expression_language/why.ipynb

@@ -36,9 +36,11 @@
    ]
   },
   {
-   "cell_type": "raw",
+   "cell_type": "code",
+   "execution_count": null,
    "id": "b99b47ec",
    "metadata": {},
+   "outputs": [],
    "source": [
     "%pip install --upgrade --quiet  langchain-core langchain-openai langchain-anthropic"
    ]