Improve netkan relationship error message

[HebaruSan]

Problem

This metadata fragment:

depends:
  - BDArmoryForRunwayProject

... produces an obscure inflation error:

362 [1] FATAL CKAN.NetKAN.Program (null) - Specified cast is not valid.

This example is from KSP-CKAN/NetKAN#9909.

Cause

An exception is thrown on this line of RelationshipsValidator:

                    foreach (JObject rel in json[relName].Cast<JObject>())

There are four main ways to loop over the children of a JSON array property:

• .Cast<T>(), which is a generic Linq function and throws an exception if any element isn't a T ("BDArmoryForRunwayProject" is a JValue, not a JObject)
• .OfType<T>(), which is a generic Linq function and ignores any element that isn't a T instead of throwing
• .Children<T>(), which is a Newtonsoft.Json function and equivalent to .OfType<T>()
• .Children(), which is a Newtonsoft.Json function and equivalent to .Children<JToken>()

We're using the wrong option from this list.

Changes

• Now we use .Children<Jobject>(), which will examine all the object children and skip the rest. If any of the others are invalid, the schema validator will catch them.
• The schema validator now outputs all on one line so the GitHub action can parse it better

  $ netkan.exe NetKAN/kOS-KerbalEngineer.netkan
  1717 [1] FATAL CKAN.NetKAN.Program (null) - Schema validation failed: #/depends[0]: ArrayItemNotValid, #/depends[1]: ArrayItemNotValid, #/depends[2]: ArrayItemNotValid, #/supports[0]: ArrayItemNotValid, #/supports[1]: ArrayItemNotValid
  

A side note, I did try catching the InvalidCastException, but it simply didn't work. The code that throws was within the try{}, the catch (InvalidCastException){} was immediately afterwards, but it continued to be caught by the outer code. I was not able to figure out why that happened.