Bump the test-dependencies group with 3 updates (#863)

Bumps the test-dependencies group with 3 updates: [NUnit](https://github.com/nunit/nunit), [Verify.NUnit](https://github.com/VerifyTests/Verify) and [Microsoft.NETFramework.ReferenceAssemblies](https://github.com/Microsoft/dotnet).


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 28.11.0 to 28.12.0
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](VerifyTests/Verify@28.11.0...28.12.0)

Updates `Microsoft.NETFramework.ReferenceAssemblies` from 1.0.3 to 1.0.3
- [Commits](https://github.com/Microsoft/dotnet/commits)

---
updated-dependencies:
- dependency-name: NUnit
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: test-dependencies
- dependency-name: Verify.NUnit
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: test-dependencies
- dependency-name: Microsoft.NETFramework.ReferenceAssemblies
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: test-dependencies
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

NGitLab.Mock.Tests/NGitLab.Mock.Tests.csproj

@@ -14,6 +14,6 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="NUnit3TestAdapter" Version="4.6.0" />
-    <PackageReference Include="Verify.NUnit" Version="28.11.0" />
+    <PackageReference Include="Verify.NUnit" Version="28.12.0" />
   </ItemGroup>
 </Project>