Bump NUnit and Verify.NUnit in /src

Bumps [NUnit](https://github.com/nunit/nunit) and [Verify.NUnit](https://github.com/VerifyTests/Verify). These dependencies needed to be updated together.

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

Updates `Verify.NUnit` from 28.6.0 to 28.6.1
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](VerifyTests/Verify@28.6.0...28.6.1)

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

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

Author: dependabot[bot]

src/Orc.Plot.Tests/Orc.Plot.Tests.csproj

@@ -27,7 +27,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="PublicApiGenerator" Version="11.3.0" PrivateAssets="all" />
-    <PackageReference Include="Verify.NUnit" Version="28.6.0" />
+    <PackageReference Include="Verify.NUnit" Version="28.6.1" />
   </ItemGroup>
 
   <ItemGroup>