Error for notify service if camera entity does not have an `access_token`

[AngellusMortis]

If a camera entity does not have an access_token attribute, calling the notify service with that camera will result in an error.

Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/helpers/script.py", line 507, in _async_step
    await getattr(self, handler)()
  File "/usr/src/homeassistant/homeassistant/helpers/script.py", line 742, in _async_call_service_step
    response_data = await self._async_run_long_action(
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/helpers/script.py", line 705, in _async_run_long_action
    return await long_task
           ^^^^^^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/core.py", line 2543, in async_call
    response_data = await coro
                    ^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/core.py", line 2580, in _execute_service
    return await target(service_call)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/components/notify/legacy.py", line 275, in _async_notify_message_service
    await self.async_send_message(**kwargs)
  File "/config/custom_components/hass_agent/notify.py", line 81, in async_send_message
    access_token = camera.attributes["access_token"]
                   ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
KeyError: 'access_token'

More context. I do not know exact what leads to access_token to not existing, but I am guessing it has something to do with the camera integration running into a timeout fetching the camera image since that seems to be what is happening to the user.