py-celery: updated to 5.2.7

5.2.7
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- Fix packaging issue which causes poetry 1.2b1 and above to fail install Celery

5.2.6
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- load_extension_class_names - correct module_name

5.2.5
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**This release was yanked due to a regression caused by the PR below**

- Use importlib instead of deprecated pkg_resources

5.2.4
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- Expose more debugging information when receiving unknown tasks

(adam)