Add NoWarn for SYSLIB0013

Don't warn on SYSLIB0013 - Uri.EscapeUriString() is obsolete.
This is marked obsolete for net6.0 and changing it to
Uri.EscapeDataString() changes behavior.  Ignore the warning.

src/Microsoft.DotNet.Arcade.Sdk/Microsoft.DotNet.Arcade.Sdk.csproj

@@ -19,7 +19,7 @@
     <EnableDefaultNoneItems>false</EnableDefaultNoneItems>
     <EnableGeneratedPackageContent>false</EnableGeneratedPackageContent>
     <_GeneratedVersionFilePath>$(IntermediateOutputPath)DefaultVersions.Generated.props</_GeneratedVersionFilePath>
-    <NoWarn>3021;NU5105</NoWarn>
+    <NoWarn>3021;NU5105;SYSLIB0013</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>