Bump NUnit (#42343)

Bumps the dotnet group in /docs/core/testing/snippets/order-unit-tests/csharp/NUnit.TestProject with 1 update: [NUnit](https://github.com/nunit/nunit).


Updates `NUnit` from 4.1.0 to 4.2.1
- [Release notes](https://github.com/nunit/nunit/releases)
- [Changelog](https://github.com/nunit/nunit/blob/main/CHANGES.md)
- [Commits](nunit/nunit@4.1.0...4.2.1)

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

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

Author: dependabot[bot]

docs/core/testing/snippets/order-unit-tests/csharp/NUnit.TestProject/NUnit.Project.csproj

@@ -8,7 +8,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="NUnit" Version="4.1.0" />
+    <PackageReference Include="NUnit" Version="4.2.1" />
     <PackageReference Include="NUnit3TestAdapter" Version="4.6.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.0" />
     <PackageReference Include="NUnit.Analyzers" Version="4.3.0">