Increase test coverage of the json library, specifically the detect_encoding() function in the __init__ module, which is used to handle the autodetection of the encoding of a bytes object passed to json.loads().

This function was added in issue 17909 which extended the json.loads() function to accept bytes.

Note that this is a small patch as I am following section 5 of the developer guide and I am trying to acquaint myself with the process as a first time contributor. I found this missing coverage just by semi-randomly looking at individual modules of interest. Please let me know if I have made any general mistakes in constructing this ticket. Thanks!