Bump NUnit3TestAdapter in /tests/NHapi.NUnit.SourceGeneration

Bumps [NUnit3TestAdapter](https://github.com/nunit/nunit3-vs-adapter) from 4.2.0 to 4.2.1.
- [Release notes](https://github.com/nunit/nunit3-vs-adapter/releases)
- [Commits](nunit/nunit3-vs-adapter@V4.2.0...V4.2.1)

---
updated-dependencies:
- dependency-name: NUnit3TestAdapter
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

tests/NHapi.NUnit.SourceGeneration/NHapi.NUnit.SourceGeneration.csproj

@@ -11,7 +11,7 @@
 
   <ItemGroup>
     <PackageReference Include="NUnit" Version="3.13.2" />
-    <PackageReference Include="NUnit3TestAdapter" Version="4.2.0" />
+    <PackageReference Include="NUnit3TestAdapter" Version="4.2.1" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
     <PackageReference Include="coverlet.collector" Version="3.1.0">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>