Fix task_defer method with non-JSON next_kwargs in TaskInstance

[dabla]

Fix serialization in task_defer method with non-JSON next_kwargs of TaskInstance as mentioned by @kaxil in PR #55068.

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Fixes TaskInstance.defer_task() so next_kwargs containing non-JSON-serializable objects (e.g., datetime, timedelta) are converted into a JSON-safe form before being persisted.

Changes:

• Serialize start_trigger_args.next_kwargs via Airflow SDK serde before assigning to TaskInstance.next_kwargs.
• Add a unit test covering defer_task() with non-JSON-native next_kwargs values.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
airflow-core/src/airflow/models/taskinstance.py	Serializes next_kwargs during deferral to avoid non-JSON values being stored.
airflow-core/tests/unit/models/test_taskinstance.py	Adds regression test verifying serde roundtrip for non-JSON next_kwargs.