Update celery requirement from ==5.4.* to ==5.6.* in /requirements

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Updates the requirements on celery to permit the latest version.

Release notes

Sourced from celery's releases.

v5.6.2

What's Changed

• Fix recursive WorkController instantiation in DjangoWorkerFixup + AttributeError when pool_cls is a string by @​bruunotrindade in celery/celery#10045
• Bugfix: Revoked tasks now immediately update backend status to REVOKED by @​Nusnus in celery/celery#9869
• Prepare for release: v5.6.2 by @​Nusnus in celery/celery#10049

New Contributors

• @​bruunotrindade made their first contribution in celery/celery#10045

Full Changelog: celery/celery@v5.6.1...v5.6.2

Changelog

Sourced from celery's changelog.

5.6.2

:release-date: 2026-01-04 :release-by: Tomer Nosrati

What's Changed

- Fix recursive WorkController instantiation in DjangoWorkerFixup + AttributeError when pool_cls is a string ([#10045](https://github.com/celery/celery/issues/10045))
- Bugfix: Revoked tasks now immediately update backend status to REVOKED ([#9869](https://github.com/celery/celery/issues/9869))
- Prepare for release: v5.6.2 ([#10049](https://github.com/celery/celery/issues/10049))
.. _version-5.6.1:
5.6.1
:release-date: 2025-12-29
:release-by: Tomer Nosrati
What's Changed

• Fix Redis Sentinel ACL authentication support (#10013)
• Fix: Broker heartbeats not sent during graceful shutdown (#9986)
• docs #5410 -- Document confirm_publish broker transport option (#10016)
• close DB pools only in prefork mode (#10020)
• Fix: Avoid unnecessary Django database connection creation during cleanup (#10015)
• reliable prefork detection (#10023)
• better coverage (#10029)
• Docs: clarify result_extended vs periodic task metadata and show headers["periodic_task_name"] example (#10030)
• Stop importing pytest_subtests (#10032)
• Only use exceptiongroup backport for Python < 3.11 (#10033)
• Prepare for release: v5.6.1 (#10037)

.. _version-5.6.0:

5.6.0

:release-date: 2025-11-30 :release-by: Tomer Nosrati

Celery v5.6.0 is now available.

Key Highlights

See :ref:`whatsnew-5.6` for a complete overview or read the main highlights below.
</tr></table> 

... (truncated)

Commits

• 6a43c84 Prepare for release: v5.6.2 (#10049)
• 333a82f Bugfix: Revoked tasks now immediately update backend status to REVOKED (#9869)
• 9d6ab11 Fix recursive WorkController instantiation in DjangoWorkerFixup + AttributeEr...
• 21dbc73 Prepare for release: v5.6.1 (#10037)
• ba20bed Only use exceptiongroup backport for Python < 3.11 (#10033)
• 2167529 Stop importing pytest_subtests
• 0527296 Bump google-cloud-firestore from 2.21.0 to 2.22.0
• 5f8659b Clarify 'result_extended' setting usage in tasks
• f19db70 Bump mypy from 1.19.0 to 1.19.1 (#10028)
• 6da72bd better coverage (#10029)
• Additional commits viewable in compare view

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