[MacOS] UI Update: Dark Mode (And Tinted) App Icon On Mac

[totalsoda]

Possibly a bug but, I don't believe that there's a dark mode app icon for NewNewsWire on the Mac app like there is on iOS.

Please implement if you get time.

Thanks

[KZeni]

I've proposed this new icon here (to go with the overall layered icon update for liquid glass which then has default, dark, clear light & dark, tinted light & dark, etc.): https://github.com/Ranchero-Software/NetNewsWire/issues/4660