chore(deps): update xunit-dotnet monorepo to v2.8.1

Author: renovate[bot]

test/Serilog.Sinks.UdpTests/Serilog.Sinks.UdpTests.csproj

@@ -20,8 +20,8 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
     <PackageReference Include="Serilog.Settings.Configuration" Version="8.0.0" />
     <PackageReference Include="Shouldly" Version="4.2.1" />
-    <PackageReference Include="xunit" Version="2.7.1" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.8">
+    <PackageReference Include="xunit" Version="2.8.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.1">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>