Bump celery from 4.4.7 to 5.0.5 in /requirements

[dependabot]

Bumps celery from 4.4.7 to 5.0.5.

Changelog

Sourced from celery's changelog.

5.0.5

:release-date: 2020-12-16 5.35 P.M UTC+2:00 :release-by: Omer Katz

• Ensure keys are strings when deleting results from S3 (#6537).
• Fix a regression breaking celery --help and celery events (#6543).

.. _version-5.0.4:

5.0.4

:release-date: 2020-12-08 2.40 P.M UTC+2:00 :release-by: Omer Katz

• DummyClient of cache+memory:// backend now shares state between threads (#6524).

  This fixes a problem when using our pytest integration with the in memory result backend. Because the state wasn't shared between threads, #6416 results in test suites hanging on result.get().

.. _version-5.0.3:

5.0.3

:release-date: 2020-12-03 6.30 P.M UTC+2:00 :release-by: Omer Katz

• Make --workdir eager for early handling (#6457).
• When using the MongoDB backend, don't cleanup if result_expires is 0 or None (#6462).
• Fix passing queues into purge command (#6469).
• Restore app.start() and app.worker_main() (#6481).
• Detaching no longer creates an extra log file (#6426).
• Result backend instances are now thread local to ensure thread safety (#6416).
• Don't upgrade click to 8.x since click-repl doesn't support it yet.
• Restore preload options (#6516).

.. _version-5.0.2:

5.0.2

:release-date: 2020-11-02 8.00 P.M UTC+2:00 :release-by: Omer Katz

• Fix _autodiscover_tasks_from_fixups (#6424).

• Flush worker prints, notably the banner (#6432).

• Breaking Change: Remove ha_policy from queue definition. (#6440)

  This argument has no effect since RabbitMQ 3.0.

... (truncated)

Commits

• 8492b75 Bump version: 5.0.4 → 5.0.5
• 8aa4eb8 Update changelog.
• 7d59e50 events.py: Remove duplicate decorator in wrong place (#6543)
• 8bceb44 Fix type error in S3 backend (#6537)
• 5fa063a fix #6047
• 420e393 Change deprecated from collections import Mapping/MutableMapping to from coll...
• 3bb2d58 Bump version: 5.0.3 → 5.0.4
• 0674684 Update changelog.
• f9ccba9 isort.
• c3e0410 DummyClient of cache+memory:// backend now shares state between threads (#6524)
• Additional commits viewable in compare view

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[dependabot]

Superseded by #91.