set the app icon for release

windows/WinUI/WinUI.csproj

@@ -55,8 +55,7 @@
     <StartupObject>WinUI.App</StartupObject>
   </PropertyGroup>
   <PropertyGroup>
-    <ApplicationIcon>
-    </ApplicationIcon>
+    <ApplicationIcon>ZeroTierIcon.ico</ApplicationIcon>
   </PropertyGroup>
   <PropertyGroup>
     <SignAssembly>false</SignAssembly>