Upgrade NUnit package to v3.13.2

Author: YevgeniyShunevych

src/Atata.Configuration.Json.Tests/Atata.Configuration.Json.Tests.csproj

@@ -17,7 +17,7 @@
     <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="3.3.0" PrivateAssets="All" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.10.0" />
     <PackageReference Include="NLog" Version="4.7.10" />
-    <PackageReference Include="NUnit" Version="3.12.0" />
+    <PackageReference Include="NUnit" Version="3.13.2" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.17.0" />
     <PackageReference Include="Selenium.WebDriver" Version="3.141.0" />
     <PackageReference Include="Selenium.WebDriver.ChromeDriver" Version="91.0.4472.1900" />