Fix the tray icon when running in a flatpak/snap sandbox

[sumwale]

Pass only the icon name rather than the path when running in a flatpak/snap sandbox since the path will not be visible in the host environment.

The upstream merged PR leanflutter/tray_manager#43 already has the change that passes through the name without the path when running in a sandbox.

[AdamVe]

@sumwale Thanks for the fix, I will merge your work 👍🏻

I will have to do some updates because of the following warning:

Import of a library in the 'lib/src' directory of another package • lib/desktop/systray.dart:25:8 • implementation_imports

[sumwale]

@AdamVe Thanks. I tested manually and missed running the test target. The tray_manager package has a pending PR leanflutter/tray_manager#78 to enhance the runningInSandbox() check for docker/podman/... containers, so wanted to avoid copying the code of the method. I suppose it should be exposed as a public API in the tray_manager package for proper usage, so will propose a PR there.

[AdamVe]

@sumwale that would be great, once that is a public API we will be happy to update the check.