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 28.7.1 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] <support@github.com>

Author: dependabot[bot]

src/Directory.Packages.props

@@ -11,8 +11,8 @@
     <PackageVersion Include="Polyfill" Version="7.11.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.147" />
     <PackageVersion Include="Ulid" Version="1.3.4" />
-    <PackageVersion Include="Verify" Version="28.7.1" />
+    <PackageVersion Include="Verify" Version="28.8.1" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.2" />
-    <PackageVersion Include="Verify.NUnit" Version="28.7.1" />
+    <PackageVersion Include="Verify.NUnit" Version="28.8.1" />
   </ItemGroup>
 </Project>