Bump Markdig from 0.38.0 to 0.39.0 in the nuget group

Bumps the nuget group with 1 update: [Markdig](https://github.com/xoofx/markdig).


Updates `Markdig` from 0.38.0 to 0.39.0
- [Release notes](https://github.com/xoofx/markdig/releases)
- [Changelog](https://github.com/xoofx/markdig/blob/master/changelog.md)
- [Commits](xoofx/markdig@0.38.0...0.39.0)

---
updated-dependencies:
- dependency-name: Markdig
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: nuget
...

Signed-off-by: dependabot[bot] <support@github.com>

src/QuestPDF.Markdown/QuestPDF.Markdown.csproj

@@ -19,7 +19,7 @@
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="Markdig" Version="0.38.0"/>
+        <PackageReference Include="Markdig" Version="0.39.0"/>
         <PackageReference Include="QuestPDF" Version="2024.12.1" />
         <PackageReference Include="SkiaSharp" Version="3.116.1" />
     </ItemGroup>