Fix JSON error typo in NakamaHTTPAdapter

[Coxcopi]

I've reported this on the forums a while ago, but there seems to have been a small typo in the NakamaHTTPAdapter.AsyncRequest parse_result() method, where it should have been

json_error

instead of

json.error

which resulted in an error message.

The reason the issue occurred is because the json.parse() method worked differently in Godot 3.x, and the code probably wasn't updated when migrating to Godot 4.

I've also included the JSON error message in the logger text to make debugging a bit easier.

[CLAassistant]

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