chore(deps): update xunit-dotnet monorepo to v2.8.1 (#768)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [xunit](https://togithub.com/xunit/xunit) | `2.8.0` -> `2.8.1` |
[![age](https://developer.mend.io/api/mc/badges/age/nuget/xunit/2.8.1?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/nuget/xunit/2.8.1?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/nuget/xunit/2.8.0/2.8.1?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/nuget/xunit/2.8.0/2.8.1?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
|
[xunit.runner.visualstudio](https://togithub.com/xunit/visualstudio.xunit)
| `2.8.0` -> `2.8.1` |
[![age](https://developer.mend.io/api/mc/badges/age/nuget/xunit.runner.visualstudio/2.8.1?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
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|
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|

---

### Release Notes

<details>
<summary>xunit/xunit (xunit)</summary>

### [`v2.8.1`](https://togithub.com/xunit/xunit/compare/2.8.0...2.8.1)

[Compare Source](https://togithub.com/xunit/xunit/compare/2.8.0...2.8.1)

</details>

<details>
<summary>xunit/visualstudio.xunit (xunit.runner.visualstudio)</summary>

###
[`v2.8.1`](https://togithub.com/xunit/visualstudio.xunit/compare/2.8.0...2.8.1)

[Compare
Source](https://togithub.com/xunit/visualstudio.xunit/compare/2.8.0...2.8.1)

</details>

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test/Directory.Build.props

@@ -11,8 +11,8 @@
     <ItemGroup>
         <PackageReference Include="FluentAssertions" Version="6.12.0" />
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
-        <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>