Bump LibGit2Sharp from 0.27.2 to 0.28.0

Bumps [LibGit2Sharp](https://github.com/libgit2/libgit2sharp) from 0.27.2 to 0.28.0.
- [Release notes](https://github.com/libgit2/libgit2sharp/releases)
- [Changelog](https://github.com/libgit2/libgit2sharp/blob/master/CHANGES.md)
- [Commits](libgit2/libgit2sharp@0.27.2...0.28.0)

---
updated-dependencies:
- dependency-name: LibGit2Sharp
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

NGitLab.Mock/NGitLab.Mock.csproj

@@ -8,7 +8,7 @@
     <ProjectReference Include="..\NGitLab\NGitLab.csproj" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="LibGit2Sharp" Version="0.27.2" />
+    <PackageReference Include="LibGit2Sharp" Version="0.28.0" />
     <PackageReference Include="Microsoft.CodeAnalysis.PublicApiAnalyzers" Version="3.3.4">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>