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 4.2.2 to 4.2.2
- [Release notes](https://github.com/nunit/nunit/releases)
- [Changelog](https://github.com/nunit/nunit/blob/main/CHANGES.md)
- [Commits](nunit/nunit@4.2.2...4.2.2)

Updates `Verify.NUnit` from 28.3.2 to 28.4.0
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](VerifyTests/Verify@28.3.2...28.4.0)

---
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]>

src/Directory.Packages.props

@@ -15,8 +15,8 @@
     <PackageVersion Include="ProjectDefaults" Version="1.0.144" />
     <PackageVersion Include="System.Diagnostics.DiagnosticSource" Version="9.0.0" />
     <PackageVersion Include="System.Runtime.Caching" Version="9.0.0" />
-    <PackageVersion Include="Verify" Version="28.3.2" />
+    <PackageVersion Include="Verify" Version="28.4.0" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.2" />
-    <PackageVersion Include="Verify.NUnit" Version="28.3.2" />
+    <PackageVersion Include="Verify.NUnit" Version="28.4.0" />
   </ItemGroup>
 </Project>