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 4.3.2 to 4.3.2
- [Release notes](https://github.com/nunit/nunit/releases)
- [Changelog](https://github.com/nunit/nunit/blob/main/CHANGES.md)
- [Commits](nunit/nunit@4.3.2...4.3.2)

Updates `Verify.NUnit` from 28.6.1 to 28.8.1
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](https://github.com/VerifyTests/Verify/commits)

---
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

@@ -17,9 +17,9 @@
     <PackageVersion Include="Syncfusion.PresentationRenderer.Net.Core" Version="28.1.35" />
     <PackageVersion Include="Syncfusion.XlsIO.Net.Core" Version="28.1.37" />
     <PackageVersion Include="Syncfusion.XlsIORenderer.Net.Core" Version="28.1.37" />
-    <PackageVersion Include="Verify" Version="28.7.0" />
+    <PackageVersion Include="Verify" Version="28.8.1" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.2" />
-    <PackageVersion Include="Verify.NUnit" Version="28.6.1" />
+    <PackageVersion Include="Verify.NUnit" Version="28.8.1" />
     <!-- CVE -->
     <PackageVersion Include="System.Text.Json" Version="9.0.0" />
     <PackageVersion Include="Microsoft.Extensions.Caching.Memory" Version="9.0.0" />