Update xunit-dotnet monorepo to v2.8.1 (#479)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

src/Cake.AzureDevOps.Tests/Cake.AzureDevOps.Tests.csproj

@@ -22,8 +22,8 @@
     <PackageReference Include="Moq" Version="4.18.4" />
     <PackageReference Include="Shouldly" Version="4.2.1" />
     <PackageReference Include="StyleCop.Analyzers" Version="1.1.118" />
-    <PackageReference Include="xunit" Version="2.8.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.0" />
+    <PackageReference Include="xunit" Version="2.8.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.1" />
   </ItemGroup>
 
   <ItemGroup>