chore(deps): update dependency microsoft.net.test.sdk to 18.4.0

| datasource | package                | from   | to     |
| ---------- | ---------------------- | ------ | ------ |
| nuget      | Microsoft.NET.Test.Sdk | 18.3.0 | 18.4.0 |

Author: renovate[bot]

UnitTests/UnitTests.csproj

@@ -11,7 +11,7 @@
 
     <ItemGroup>
         <PackageReference Include="JunitXml.TestLogger" Version="7.1.0" />
-        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
         <PackageReference Include="xunit" Version="2.9.3" />
         <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5" />
         <ProjectReference Include="..\CSSParser\CSSParser.csproj" />