Bump Markdig from 1.4.2 to 1.5.1

---
updated-dependencies:
- dependency-name: Markdig
  dependency-version: 1.5.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

src/GitHubConnector.csproj

@@ -25,7 +25,7 @@
 
   <ItemGroup>
     <PackageReference Include="Azure.Identity" Version="1.21.0" />
-    <PackageReference Include="Markdig" Version="1.4.2" />
+    <PackageReference Include="Markdig" Version="1.5.1" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="10.0.13" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="10.0.13" />
     <PackageReference Include="Microsoft.Extensions.Configuration.UserSecrets" Version="10.0.13" />