Flatpak building guide links incorrectly to pre-release Debian page

[rugk]

https://github.com/tauri-apps/tauri-docs/blob/c2398b2231a8b32eea05565f764aef06db1b8c9b/src/content/docs/distribute/flatpak.mdx?plain=1#L60

As you can see, this link is wrong.

Should it point to https://v2.tauri.app/distribute/debian/ possibly? Though that is a stub so hmm…