Bump NUnit from 4.3.0 to 4.3.1 in /source

Bumps [NUnit](https://github.com/nunit/nunit) from 4.3.0 to 4.3.1.
- [Release notes](https://github.com/nunit/nunit/releases)
- [Changelog](https://github.com/nunit/nunit/blob/main/CHANGES.md)
- [Commits](nunit/nunit@4.3.0...4.3.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

source/TestProject/TestProject.csproj

@@ -24,7 +24,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
-    <PackageReference Include="NUnit" Version="4.3.0" />
+    <PackageReference Include="NUnit" Version="4.3.1" />
     <PackageReference Include="NUnit3TestAdapter" Version="4.6.0" />
     <PackageReference Include="NUnit.Analyzers" Version="4.4.0" />
     <PackageReference Include="coverlet.collector" Version="6.0.2" />