Bump xunit from 2.8.0 to 2.8.1 in /csharp/unit-testing/XUnit.TestProj…

…ect (#6929)

Bumps [xunit](https://github.com/xunit/xunit) from 2.8.0 to 2.8.1.
- [Commits](xunit/xunit@2.8.0...2.8.1)

---
updated-dependencies:
- dependency-name: xunit
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Bill Wagner <wiwagn@microsoft.com>

csharp/unit-testing/XUnit.TestProject/XUnit.Project.csproj

@@ -8,7 +8,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
-    <PackageReference Include="xunit" Version="2.8.0" />
+    <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>