Bump Microsoft.NET.Test.Sdk from 17.11.1 to 17.12.0 in /src (#326)

Author: dependabot[bot]

src/Directory.Packages.props

@@ -5,7 +5,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="MarkdownSnippets.MsBuild" Version="27.0.2" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageVersion Include="Polyfill" Version="7.4.1" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.144" />
     <PackageVersion Include="Verify" Version="28.3.2" />