chore(deps): update dependency xunit.runner.visualstudio to 3.1.3

| datasource | package                   | from  | to    |
| ---------- | ------------------------- | ----- | ----- |
| nuget      | xunit.runner.visualstudio | 3.1.2 | 3.1.3 |

Author: renovate[bot]

UnitTests/UnitTests.csproj

@@ -11,7 +11,7 @@
     <ItemGroup>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
         <PackageReference Include="xunit" Version="2.9.3" />
-        <PackageReference Include="xunit.runner.visualstudio" Version="3.1.2" />
+        <PackageReference Include="xunit.runner.visualstudio" Version="3.1.3" />
         <ProjectReference Include="..\CSSParser\CSSParser.csproj" />
         <ProjectReference Include="..\CSSParser.ExtendedLESSParser\CSSParser.ExtendedLESSParser.csproj" />
     </ItemGroup>