Treat CS1591 and CS1574 as warnings, not errors

Author: Arlodotexe

Directory.Build.props

@@ -15,7 +15,7 @@
     <NoWarn>$(NoWarn);Uno0001</NoWarn>
 
     <!-- See https://github.com/CommunityToolkit/Labs-Windows/pull/605#issuecomment-2498743676 -->
-    <WarningsNotAsErrors>NU1901;NU1902;NU1903;NU1904</WarningsNotAsErrors>
+    <WarningsNotAsErrors>NU1901;NU1902;NU1903;NU1904;CS1591;CS1574</WarningsNotAsErrors>
   </PropertyGroup>
 
   <Import Project="Windows.Toolkit.Common.props" />