Bump MarkdownSnippets.MsBuild from 28.0.0-beta.11 to 28.0.0-beta.18

---
updated-dependencies:
- dependency-name: MarkdownSnippets.MsBuild
  dependency-version: 28.0.0-beta.18
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

src/Directory.Packages.props

@@ -5,7 +5,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="FakeItEasy" Version="9.0.0" />
-    <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.0.0-beta.11" />
+    <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.0.0-beta.18" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
     <PackageVersion Include="Polyfill" Version="9.7.3" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.170" />