fix portfolio optimization example

optimization/05_portfolio_optimization.py

@@ -245,3 +245,13 @@ def _(gamma, gamma_vals, markers_on, np, plt, prob, ret, risk):
     plt.legend(loc="upper right")
     plt.show()
     return midx, spstats, x
+
+
+@app.cell
+def _():
+    import marimo as mo
+    return (mo,)
+
+
+if __name__ == "__main__":
+    app.run()