Bump MarkdownSnippets.MsBuild from 28.0.0-beta.5 to 28.0.0-beta.6

---
updated-dependencies:
- dependency-name: MarkdownSnippets.MsBuild
  dependency-version: 28.0.0-beta.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

src/Directory.Packages.props

@@ -4,7 +4,7 @@
     <CentralPackageTransitivePinningEnabled>true</CentralPackageTransitivePinningEnabled>
   </PropertyGroup>
   <ItemGroup>
-    <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.0.0-beta.5" />
+    <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.0.0-beta.6" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.0" />
     <PackageVersion Include="Polyfill" Version="8.9.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.161" />