Bump Newtonsoft.Json in /src/csharp/Grpc.Tools.Tests (#32047)

Bumps [Newtonsoft.Json](https://github.com/JamesNK/Newtonsoft.Json) from 9.0.1 to 13.0.1.
- [Release notes](https://github.com/JamesNK/Newtonsoft.Json/releases)
- [Commits](https://github.com/JamesNK/Newtonsoft.Json/compare/9.0.1...13.0.1)

---
updated-dependencies:
- dependency-name: Newtonsoft.Json
  dependency-type: direct:production
...

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src/csharp/Grpc.Tools.Tests/Grpc.Tools.Tests.csproj

@@ -21,7 +21,7 @@
 
   <ItemGroup>
     <PackageReference Include="Moq" Version="4.8.3" />
-    <PackageReference Include="Newtonsoft.Json" Version="9.0.1" />
+    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
     <PackageReference Include="NUnit; NUnitLite" Version="3.10.1" />
     <PackageReference Include="System.Runtime.InteropServices.RuntimeInformation" Version="4.3.0" />
   </ItemGroup>