nuget: bump xunit in /DotMP-Tests in the xunit group across 1 directory

Bumps the xunit group with 1 update in the /DotMP-Tests directory: [xunit](https://github.com/xunit/xunit).


Updates `xunit` from 2.7.1 to 2.8.1
- [Commits](xunit/xunit@2.7.1...2.8.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

DotMP-Tests/DotMP-Tests.csproj

@@ -19,8 +19,8 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
-    <PackageReference Include="xunit" Version="2.7.1" />
-    <PackageReference Include="xunit.analyzers" Version="1.12.0" />
+    <PackageReference Include="xunit" Version="2.8.1" />
+    <PackageReference Include="xunit.analyzers" Version="1.14.0" />
     <PackageReference Include="xunit.core" Version="2.7.1" />
     <PackageReference Include="xunit.runner.console" Version="2.7.1">
       <PrivateAssets>all</PrivateAssets>