internal/ui: data race in tray icon handling

[DeedleFake]

trayscale/internal/ui/app.go

Lines 350 to 352 in 764e58c

	if a.tray == nil {
	a.tray = tray.New(a.online)
	}

trayscale/internal/ui/app.go

Line 182 in 764e58c

a.tray.Update(s, a.online)

The above read and write of a.tray happen concurrently and are not synchronized. This is an extremely unlikely problem considering the way that initialization happens, but it's still technically a bug and should be fixed.