Bump Microsoft.NET.Test.Sdk from 18.5.1 to 18.6.0 (#338)

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.6.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]

src/Directory.Packages.props

@@ -6,7 +6,7 @@
   <ItemGroup>
     <PackageVersion Include="FluentValidation" Version="12.1.1" />
     <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.2.0" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.5.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.6.0" />
     <PackageVersion Include="Microsoft.Sbom.Targets" Version="4.1.5" />
     <PackageVersion Include="NUnit" Version="4.6.1" />
     <PackageVersion Include="NUnit3TestAdapter" Version="6.2.0" />