Update/remove Gunicorn freeze

[torgeirl]

pyproject.toml has freezed Gunicorn to v19.9.*, and that makes Devilry incompatible with django-storages for S3 (includes boto3) when running Python 3.10+:

Error: class uri 'gunicorn.workers.gthread.ThreadWorker' invalid or not found: 

[Traceback (most recent call last):
  File "/usr/local/lib/python3.10/site-packages/gunicorn/workers/gthread.py", line 40, in <module>
    from asyncio import selectors
ImportError: cannot import name 'selectors' from 'asyncio' (/usr/local/lib/python3.10/asyncio/__init__.py)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.10/site-packages/gunicorn/util.py", line 135, in load_class
    mod = import_module('.'.join(components))
  File "/usr/local/lib/python3.10/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 883, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/usr/local/lib/python3.10/site-packages/gunicorn/workers/gthread.py", line 42, in <module>
    from gunicorn import selectors
  File "/usr/local/lib/python3.10/site-packages/gunicorn/selectors.py", line 11, in <module>
    from collections import namedtuple, Mapping
ImportError: cannot import name 'Mapping' from 'collections' (/usr/local/lib/python3.10/collections/__init__.py)
]

---

Another possible related issue caused by this is that custom logging for Gunicorn doesn't work for the request time in milliseconds (%(M)s).

[Levijatan]

Could not find any reason why gunicorn where frozen to 19 and could not find any applicable breaking changes inn the gunicorn changelog so upped it to 21.

[torgeirl]

Solved in ae6b54097e5983a90317ffb668e02519bad414a9.