Fix: Added example of _push_xcoms_if_necessary to deferring.rst

[avyuktsoni0731]

---

What is the purpose of this PR?

This PR updates the deferring.rst documentation to include an example of the _push_xcoms_if_necessary method, as suggested in issue #44759.

The new content provides guidance on:

• Pushing XComs when deferred tasks exit directly from triggers.
• How to integrate _push_xcoms_if_necessary with custom triggers.

Related Issues

Closes #44759.

Changes Made

• Added a new section under Exiting deferred task from Triggers in deferring.rst to describe the _push_xcoms_if_necessary method and its usage.
• Included example code snippets to illustrate the implementation.

Checklist

• Documentation updated.
• Code quality checks passed (pre-commit hooks run).

Reviewers

Please suggest any further refinements or additional examples if required.

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[potiuk]

@tirkarthi @eladkal -> I think you were more involved in #44759 - that one looks nice and good I will have a few nits.

[potiuk]

Hmm. I am not sure how to get the task instance here . I am not sure if you can do it automatically ?

[avyuktsoni0731]

Right, let me look into this again, and try to make the necessary changes that @tirkarthi suggested.

[tirkarthi]

I don't think this is the right approach. My comment was that you can set self.xcoms which is a dictionary and then the triggerer pushes it to xcom once the event is emitted. There is no need to reimplement _push_xcoms_if_necessary or even mention it as a public interface. The example would be to set self.xcoms and explain to users that triggerer does the job of pushing them to xcom.

#44759 (comment)

[avyuktsoni0731]

@potiuk @tirkarthi I've created a PR with the changes, please do look into it, and let me know if I'm still not able to understand it properly, will make the required changes if needed.

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