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 28.5.0 to 28.6.0
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](VerifyTests/Verify@28.5.0...28.6.0)

---
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-minor
...

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

Author: dependabot[bot]

src/Directory.Packages.props

@@ -10,8 +10,8 @@
     <PackageVersion Include="NUnit3TestAdapter" Version="4.6.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.147" />
     <PackageVersion Include="SixLabors.ImageSharp" Version="3.1.6" />
-    <PackageVersion Include="Verify" Version="28.5.0" />
+    <PackageVersion Include="Verify" Version="28.6.0" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.2" />
-    <PackageVersion Include="Verify.Nunit" Version="28.5.0" />
+    <PackageVersion Include="Verify.Nunit" Version="28.6.0" />
   </ItemGroup>
 </Project>