Update xunit-dotnet monorepo to v2.8.1

Author: renovate[bot]

System.IO.Abstractions.Analyzers.Tests/System.IO.Abstractions.Analyzers.Tests.csproj

@@ -9,8 +9,8 @@
 	<ItemGroup>
 		<PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.6.3" />
 		<PackageReference Include="System.IO.Abstractions" Version="19.1.14" />
-		<PackageReference Include="xunit" Version="2.6.2" />
-		<PackageReference Include="xunit.runner.visualstudio" Version="2.5.4">
+		<PackageReference Include="xunit" Version="2.8.1" />
+		<PackageReference Include="xunit.runner.visualstudio" Version="2.8.1">
 		  <PrivateAssets>all</PrivateAssets>
 		  <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
 		</PackageReference>