Bump nunit (#42336)

Bumps the dotnet group in /samples/snippets/core/testing/unit-testing-using-nunit/csharp 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]

samples/snippets/core/testing/unit-testing-using-nunit/csharp/PrimeService.Tests/PrimeService.Tests.csproj

@@ -9,7 +9,7 @@
 
   <!--<snippetPackages>-->
   <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">