fix window icon for linux

[laur89]

fixes #1978

Pre-flight Checklist

Please ensure you've completed all of the following.

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.

Description of Change

This change adds icon property to main BrowserWindow config, given the build is for linux.

Motivation and Context

This change adds window icon for some window manager under linux that were broken until now, e.g. i3wm.
For context see #1978 or brief conversation on discord

Screenshots

See the related issue #1978

Checklist

• My pull request is properly named
• The changes respect the code style of the project (pnpm prepare-code)
• pnpm test passes
• I tested/previewed my changes locally

Note the two items are not checked as I built it via Dockerfile

Release Notes

Fix window icon for some Linux window managers (e.g. i3wm)

[Alphrag]

Tested on cross-platforms (Windows, MacOS and Linux Debian) and it works as expected. Thanks @laur89!