Two components of the boundary of \(\text \textbf{I}_3\). (Deux composantes du bord de \(\text \textbf{I}_3\)) A splitting theorem for the Kupka component of a foliation of \({\mathbb{C}} {\mathbb{P}}^ n, n\geq 6\). Addendum to a paper by O. Calvo-Andrade and M. Soares 