Update dependency xunit to v2.8.0

Author: renovate[bot]

Directory.Build.props

@@ -49,7 +49,7 @@
 
   <ItemGroup Condition="'$(IsTestProject)' == 'true'">
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
-    <PackageReference Include="xunit" Version="2.7.0" />
+    <PackageReference Include="xunit" Version="2.8.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.7">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>