Bump Newtonsoft.Json in /src/Swashbuckle.AspNetCore.ApiTesting

Bumps [Newtonsoft.Json](https://github.com/JamesNK/Newtonsoft.Json) from 12.0.3 to 13.0.1.
- [Release notes](https://github.com/JamesNK/Newtonsoft.Json/releases)
- [Commits](JamesNK/Newtonsoft.Json@12.0.3...13.0.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

src/Swashbuckle.AspNetCore.ApiTesting/Swashbuckle.AspNetCore.ApiTesting.csproj

@@ -25,7 +25,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
+    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
     <PackageReference Include="Microsoft.OpenApi" Version="1.2.3" />
     <PackageReference Include="Microsoft.OpenApi.Readers" Version="1.2.3" />
   </ItemGroup>