Fix Dataflow sensors losing their XCom value when not deferred

[FrankYang0529]

Why

• DataflowJobMessagesSensor, DataflowJobAutoScalingEventsSensor and DataflowJobMetricsSensor return their payload to XCom when deferred, but drop it in poke mode. deferrable defaults to False, so the default path is the broken one.

• The payload travels through a chain, and these sensors break it at the last step:

  poke()                          →  PokeReturnValue(is_done=True, xcom_value=X)
  BaseSensorOperator.execute()    →  picks X out and returns it
  subclass execute()              →  must return it upwards        ← dropped here
  task runner                     →  pushes it as the return_value XCom
  

How

• Return super().execute(context) from the three sensors' execute() overrides.
• Wrap DataflowJobMetricsSensor.poke()'s result in PokeReturnValue, the same way Bugfix/return DataflowJobMessagesSensor and DataflowJobAutoScalingEventsSensor result with xcom_value #53115 did for the other two.

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

• Yes - Claude Code

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[molcay]

Hi @FrankYang0529,

Thank you for your change. It is very much appreciated!

From my side, it seems a good change. However we want to see the system tests run results before merging a change.

Did you run the system tests? Can you share the results of the system tests?

[FrankYang0529]

Did you run the system tests? Can you share the results of the system tests?

@molcay Thanks for the suggestion. I add a xcom assertion to system test and make sure it passes on this branch, but fails on main branch.