fix: render warning as blockquote in tutorial 50

Author: kacperlukawski

tutorials/50_Using_Pre_Built_Agents_from_Agent_Pack.ipynb

@@ -45,11 +45,7 @@
    "cell_type": "markdown",
    "id": "a1114b46",
    "metadata": {},
-   "source": [
-    ":::warning\n",
-    "**Agent Pack is experimental.** Its APIs and agent architectures can change in any release, without following the usual Haystack deprecation policy. It is distributed separately from `haystack-ai` (in [`haystack-core-integrations`](https://github.com/deepset-ai/haystack-core-integrations)) precisely so these patterns can evolve quickly. Expect things to change and occasionally break, and pin a version if you depend on it in production.\n",
-    ":::"
-   ]
+   "source": "> ⚠️ **Agent Pack is experimental.** Its APIs and agent architectures can change in any release, without following the usual Haystack deprecation policy. It is distributed separately from `haystack-ai` (in [`haystack-core-integrations`](https://github.com/deepset-ai/haystack-core-integrations)) precisely so these patterns can evolve quickly. Expect things to change and occasionally break, and pin a version if you depend on it in production."
   },
   {
    "cell_type": "markdown",