In RestRequest.executeUnparsed(), if we get a bad HTTP response code, we try to extract the error message from the response by parsing it as JSON. Github will sometimes not respond with JSON but instead with a webpage, which fails to parse. This failure to parse is thrown as an IllegalStateException which is not always handled well in layers above.

We need to catch any exception caused by failing to parse the message as JSON so that they do not hide the real UncheckedRestException.