updated reference header

Co-authored-by: Akshay Agrawal <akshaykagrawal7@gmail.com>

Author: koushikkhan

polars/01_why_polars.py

@@ -286,7 +286,7 @@ def _(mo):
 def _(mo):
     mo.md(
         """
-        # 🔖 References
+        ## 🔖 References
 
         - [Polars official website](https://pola.rs/)
         - [Polars vs. Pandas](https://blog.jetbrains.com/pycharm/2024/07/polars-vs-pandas/)