Bump the dotnet group in /tools with 2 updates (#1122)

Bumps the dotnet group in /tools with 2 updates: [xunit](https://github.com/xunit/xunit) and [xunit.runner.visualstudio](https://github.com/xunit/visualstudio.xunit).


Updates `xunit` from 2.8.0 to 2.8.1
- [Commits](xunit/xunit@2.8.0...2.8.1)

Updates `xunit.runner.visualstudio` from 2.8.0 to 2.8.1
- [Release notes](https://github.com/xunit/visualstudio.xunit/releases)
- [Commits](xunit/visualstudio.xunit@2.8.0...2.8.1)

---
updated-dependencies:
- dependency-name: xunit
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dotnet
- dependency-name: xunit.runner.visualstudio
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dotnet
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

tools/MarkdownConverter.Tests/MarkdownConverter.Tests.csproj

@@ -15,8 +15,8 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
     <PackageReference Include="XMLUnit.Core" Version="2.9.2" />
-    <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">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>