fix: patching in fakesnow.ipynb

it wasn't working because the finally was undoing the patching when the
context manager was garbage collected

now we hold the reference p to avoid this

notebooks/fakesnow.ipynb

@@ -25,7 +25,8 @@
     "\n",
     "import fakesnow\n",
     "\n",
-    "fakesnow.patch().__enter__()\n",
+    "p = fakesnow.patch()\n",
+    "p.__enter__()\n",
     "conn = snowflake.connector.connect(database='db1', schema='schema1')\n",
     "cur = conn.cursor()\n",
     "print(cur.execute(\"SELECT 'Hello fake world!'\").fetchone())\n"