Since the message might have been delivered to the wrong worker due to a
routing error,
we need to emit the headers and delivery_info when logging the error as
well as the message's body.

This avoids runtime dependency on setuptools.

* load_extension_class_names - correct module_name

95015a changed over to using importlib rather than pkg_resources,
unfortunately the object is not exactly the same.

Attempting to start up a celery instance with `django-celery-results`
installed results in an exception during `load_extension_class_names`;

```
During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.10/site-packages/celery/worker/worker.py", line 203, in start
    self.blueprint.start(self)
  File "/usr/lib/python3.10/site-packages/celery/bootsteps.py", line 112, in start
    self.on_start()
  File "/usr/lib/python3.10/site-packages/celery/apps/worker.py", line 136, in on_start
    self.emit_banner()
  File "/usr/lib/python3.10/site-packages/celery/apps/worker.py", line 170, in emit_banner
    ' \n', self.startup_info(artlines=not use_image))),
  File "/usr/lib/python3.10/site-packages/celery/apps/worker.py", line 232, in startup_info
    results=self.app.backend.as_uri(),
  File "/usr/lib/python3.10/site-packages/celery/app/base.py", line 1252, in backend
    self._local.backend = new_backend = self._get_backend()
  File "/usr/lib/python3.10/site-packages/celery/app/base.py", line 955, in _get_backend
    backend, url = backends.by_url(
  File "/usr/lib/python3.10/site-packages/celery/app/backends.py", line 69, in by_url
    return by_name(backend, loader), url
  File "/usr/lib/python3.10/site-packages/celery/app/backends.py", line 47, in by_name
    aliases.update(load_extension_class_names(extension_namespace))
  File "/usr/lib/python3.10/site-packages/celery/utils/imports.py", line 146, in load_extension_class_names
    yield ep.name, ':'.join([ep.module_name, ep.attrs[0]])
AttributeError: 'EntryPoint' object has no attribute 'module_name'
```

Move over to using the direct value should resolve this issue;

```
>>> from pkg_resources import iter_entry_points
>>> list(iter_entry_points('celery.result_backends'))[0].__dict__
{'name': 'django-cache', 'module_name': 'django_celery_results.backends', 'attrs': ('CacheBackend',), 'extras': (), 'dist': django-celery-results 2.3.0 (/usr/lib/python3.10/site-packages)}
```
vs
```
>>> from importlib.metadata import entry_points
>>> entry_points().get('celery.result_backends')[0]
EntryPoint(name='django-cache', value='django_celery_results.backends:CacheBackend', group='celery.result_backends')
```

* Update changelog.

Co-authored-by: Damian Zaremba <[email protected]>
Co-authored-by: Omer Katz <[email protected]>

This reverts commit 272b534.