[bug] App icon is not used in .deb build

Describe the bug

After generating icon files using the tauri icon from a provided PNG and running tauri build, the .deb build does not have any icon at all (.AppImage is fine!)

Reproduction

https://github.com/moritree/tauri-linux-icon-mre

Steps taken:

1. Create fresh project with yarn create tauri-app. Basic settings: TypeScript, yarn, vanilla UI.
2. Add icon to root folder at app-icon.png
3. Run yarn tauri icon app-icon.png
4. yarn tauri build; install .deb package

Expected behavior

No response

Full tauri info output

[✔] Environment
    - OS: Ubuntu 24.10.0 x86_64 (X64) (KDE on wayland)
    ✔ webkit2gtk-4.1: 2.48.1
    ✔ rsvg2: 2.59.1
    ✔ rustc: 1.86.0 (05f9846f8 2025-03-31)
    ✔ cargo: 1.86.0 (adf9b6ad1 2025-02-28)
    ✔ rustup: 1.28.2 (e4f3ad6f8 2025-04-28)
    ✔ Rust toolchain: stable-x86_64-unknown-linux-gnu (default)
    - node: 20.16.0
    - yarn: 1.22.22
    - npm: 9.2.0

[-] Packages
    - tauri 🦀: 2.5.1
    - tauri-build 🦀: 2.2.0
    - wry 🦀: 0.51.2
    - tao 🦀: 0.33.0
    - tauri-cli 🦀: 2.5.0
    - @tauri-apps/api : 2.5.0
    - @tauri-apps/cli : 2.5.0

[-] Plugins
    - tauri-plugin-opener 🦀: 2.2.6
    - @tauri-apps/plugin-opener : 2.2.6

[-] App
    - build-type: bundle
    - CSP: unset
    - frontendDist: ../dist
    - devUrl: http://localhost:1420/
    - bundler: Vite

Stack trace

Additional context

No response

Start with the minimal reproduction at https://github.com/moritree/tauri-linux-icon-mre and repeat yarn tauri icon app-icon.png followed by yarn tauri build. Compare the generated .deb with the working .AppImage; done means the installed Debian package uses the generated application icon.