[NWD][Security] Update Newtonsoft.json dependency in Test package

Snyk: https://security.snyk.io/vuln/SNYK-DOTNET-NEWTONSOFTJSON-2774678

Testing: NetCoreTests passed successfuly

Part of: b/230278644
Release Notes: no
Rollout: no

Change-Id: Ic3b083e952e602a3312b13fcaddd65d834ac8fd6

NetCoreTests/NetCoreTests.csproj

diff --git a/NetCoreTests/NetCoreTests.csproj b/NetCoreTests/NetCoreTests.csproj
index 4ae4dbc..95aa3fb 100644
--- a/NetCoreTests/NetCoreTests.csproj
+++ b/NetCoreTests/NetCoreTests.csproj
@@ -16,5 +16,8 @@
     <ProjectReference Include="..\EPPlus\EPPlusSDK.csproj" />
     
     <None Include="TestWorkbooks/**" CopyToOutputDirectory="PreserveNewest"/>
+
+    <!--Transient dependency; required to address b/230278644-->
+    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
   </ItemGroup>
 </Project>