Fix celery provider ImportError on airflow 3.2.x by gating ExecutorWorkload on 3.3+

[anishgirianish]

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celery_executor_utils.execute_workload gates the new ExecutorWorkload / BaseExecutor.run_workload path on AIRFLOW_V_3_2_PLUS, but both symbols were only added on main (3.3+). On airflow 3.2.0 every celery task fails with:

ImportError: cannot import name 'ExecutorWorkload' from 'airflow.executors.workloads'

Fix: add AIRFLOW_V_3_3_PLUS and move the gate (+ rename the fallback helper to _execute_workload_pre_3_3).

Surfaced while verifying #65702 (celery 3.19.0rc1). Regression from #62645.

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[anishgirianish]

cc: @shahar1 @ferruzzi

[potiuk]

I think we should add some executor tests with compatibility tests. We do not seem to test compatibility for executors in our compat tests. It's the second time when the tests were not catching something I think.

Anyone could take a look maybe?

[hussein-awala]

I think we should add some executor tests with compatibility tests

+1