Make test_celery_integration runnable

[eladkal]

It looks like the Celery test was never executed due to return statement.
once removed the test started to run but discovered that it doesn't pass.
Hopefully I fixed all the issues and now it should pass

Here's a summary of all the fixes made to test_celery_executor.py:

1. Moved test_celery_integration, test_error_sending_task, and test_retry_on_error_sending_task out of the dead-code helper function and into TestCeleryExecutor as proper methods.
2. Inlined the dag setup directly in test_celery_integration instead of using a separate helper (per your suggestion).
3. Derived TaskInstanceKeys from the actual dagrun task instances instead of using hardcoded mismatched values.
4. Replaced ExecuteTask.make() (which requires ORM relationships) with explicit ExecuteTask(...) construction with all required fields.
5. Fixed the sort destructuring order — "fail" sorts before "success" alphabetically.
6. Set executor._sync_parallelism = 1 so task sending stays in the main thread where mock patches are active.

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Was generative AI tooling used to co-author this PR?

• [v] Yes (please specify the tool below)
  Claude Opus 4.6

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