Bump Microsoft.NET.Test.Sdk from 18.3.0 to 18.4.0

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.4.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

src/Directory.Packages.props

@@ -6,7 +6,7 @@
   <ItemGroup>
     <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.0.2" />
     <PackageVersion Include="Microsoft.CSharp" Version="4.7.0" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
     <PackageVersion Include="OpenMcdf" Version="3.1.2" />
     <PackageVersion Include="Polyfill" Version="9.23.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.172" />