Stop testing on mono

Author: AArnott

test/VS.Mefx.Tests/VS.Mefx.Tests.csproj

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net8.0;net472</TargetFrameworks>
+    <TargetFrameworks>net8.0</TargetFrameworks>
+    <TargetFrameworks Condition="$([MSBuild]::IsOSPlatform('Windows'))">$(TargetFrameworks);net472</TargetFrameworks>
     <AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects>
     <GenerateBindingRedirectsOutputType>true</GenerateBindingRedirectsOutputType>
   </PropertyGroup>