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 28.2.1 to 28.3.1
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](VerifyTests/Verify@28.2.1...28.3.1)

---
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-minor
...

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

src/Directory.Packages.props

@@ -11,7 +11,7 @@
     <PackageVersion Include="NUnit3TestAdapter" Version="4.6.0" />
     <PackageVersion Include="Polyfill" Version="7.4.1" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.144" />
-    <PackageVersion Include="Verify" Version="28.2.1" />
-    <PackageVersion Include="Verify.Nunit" Version="28.2.1" />
+    <PackageVersion Include="Verify" Version="28.3.1" />
+    <PackageVersion Include="Verify.Nunit" Version="28.3.1" />
   </ItemGroup>
 </Project>