Drop back xunit versions temporarily to attempt a build fix

Author: nblumhardt

test/Serilog.Sinks.OpenTelemetry.Tests/Serilog.Sinks.OpenTelemetry.Tests.csproj

@@ -24,8 +24,8 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="3.0.2" PrivateAssets="all" />
-    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.0" PrivateAssets="all" />
+    <PackageReference Include="xunit" Version="2.8.0" />
     <PackageReference Include="PublicApiGenerator" Version="11.4.5" />
     <PackageReference Include="Shouldly" Version="4.3.0" />
     <PackageReference Include="OpenTelemetry.SemanticConventions" Version="1.0.0-rc9.9" />