chore(deps): update dependency microsoft.net.test.sdk to v18 (#142)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

UnitTests/UnitTests.csproj

@@ -11,7 +11,7 @@
 
     <ItemGroup>
         <PackageReference Include="JunitXml.TestLogger" Version="7.0.2" />
-        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.0" />
         <PackageReference Include="xunit" Version="2.9.3" />
         <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5" />
         <ProjectReference Include="..\CSSParser\CSSParser.csproj" />