Fixed xunit version to 2.4.2 for netcoreapp3.1'

Author: tmatthey

src/NetMQ.Tests/NetMQ.Tests.csproj

@@ -15,7 +15,7 @@
     <!-- have to teachcd MSBuild where the Mono copy of the reference asssemblies is -->
     <TargetIsMono Condition="$(TargetFramework.StartsWith('net4')) and '$(OS)' == 'Unix'">true</TargetIsMono>
 
-      <!-- Look in the standard install locations -->
+    <!-- Look in the standard install locations -->
     <BaseFrameworkPathOverrideForMono Condition="'$(BaseFrameworkPathOverrideForMono)' == '' AND '$(TargetIsMono)' == 'true' AND EXISTS('/Library/Frameworks/Mono.framework/Versions/Current/lib/mono')">/Library/Frameworks/Mono.framework/Versions/Current/lib/mono</BaseFrameworkPathOverrideForMono>
     <BaseFrameworkPathOverrideForMono Condition="'$(BaseFrameworkPathOverrideForMono)' == '' AND '$(TargetIsMono)' == 'true' AND EXISTS('/usr/lib/mono')">/usr/lib/mono</BaseFrameworkPathOverrideForMono>
     <BaseFrameworkPathOverrideForMono Condition="'$(BaseFrameworkPathOverrideForMono)' == '' AND '$(TargetIsMono)' == 'true' AND EXISTS('/usr/local/lib/mono')">/usr/local/lib/mono</BaseFrameworkPathOverrideForMono>
@@ -41,15 +41,26 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
+  </ItemGroup>
+
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net47' ">
+    <PackageReference Include="ZeroMQ" Version="4.1.0.31" />
+  </ItemGroup>
+
+  <ItemGroup Condition=" '$(TargetFramework)' != 'netcoreapp3.1' ">
     <PackageReference Include="xunit" Version="2.8.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
   </ItemGroup>
-  
-  <ItemGroup Condition=" '$(TargetFramework)' == 'net47' ">
-    <PackageReference Include="ZeroMQ" Version="4.1.0.31" />
+
+  <ItemGroup Condition=" '$(TargetFramework)' == 'netcoreapp3.1' ">
+    <PackageReference Include="xunit" Version="2.4.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
   </ItemGroup>
 
 </Project>