Fix Emby notifier error on Python 3

[sharkykh]

From #7486

Traceback (most recent call last):
  File "/app/medusa/medusa/server/web/core/base.py", line 251, in async_call
    result = function(**kwargs)
  File "/app/medusa/medusa/server/web/home/handler.py", line 434, in testEMBY
    result = notifiers.emby_notifier.test_notify(unquote_plus(host), emby_apikey)
  File "/app/medusa/medusa/notifiers/emby.py", line 80, in test_notify
    return self._notify_emby('This is a test notification from Medusa', host, emby_apikey)
  File "/app/medusa/medusa/notifiers/emby.py", line 60, in _notify_emby
    log.debug('EMBY: HTTP response: {0}', resp.content.replace('\n', ''))
TypeError: a bytes-like object is required, not 'str'

Fixes #7339 too, it seems.