Bump NJsonSchema and fix related

[danzel]

We are updating our project to .net 6. It uses nswag and sigspec to generate csharp and typescript clients on startup.

Using them both together under .net 6 didn't work as the version of namotion.reflection differs by a lot. To resolve this I've updated NJsonSchema to the latest version here, matching nswag.

This led me to find a few more issues:

• The templates have elseif but should have elsif.
• The njsonschema template cache is shared between nswag and sigspec, so once nswag has loaded the ("Typescript", "File") -> "File.liquid" template, then when sigspec tries to load its own it will instead receive the nswag template file. I've worked around this by renaming File.liquid to HubFile.liquid

Thanks!

[RicoSuter]

Already updated. Thanks for the PR