Bump NUnit from 4.1.0 to 4.2.1

Bumps [NUnit](https://github.com/nunit/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
...

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

BadMedicine.Dicom.Tests/BadMedicine.Dicom.Tests.csproj

@@ -15,7 +15,7 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
-    <PackageReference Include="NUnit" Version="4.1.0" />
+    <PackageReference Include="NUnit" Version="4.2.1" />
     <PackageReference Include="NUnit.Analyzers" Version="4.3.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>