Keep triggerer alive when deferred tasks disappear

[idan192]

A stale deferred task can raise TaskNotFound while the triggerer loads its pinned serialized Dag, aborting workload construction for unrelated triggers in the same supervisor batch.

Catch only that task lookup failure, emit the trigger and task-instance identifiers as structured fields, and construct the ordinary context-free workload. Direct-to-triggerer tasks that still exist continue to receive Dag and DagRun context unchanged.

The durable context-requirement persistence change is tracked in #69841. This PR is deliberately small and backportable; please cherry-pick it to v3-3-test for the next 3.3.x release.

Validation

• A missing task now produces a context-free workload and all structured identifiers are present.
• A mixed stale/healthy batch constructs both workloads; the healthy direct-to-triggerer workload retains Dag and DagRun data.
• Diff-scoped pre-commit and manual hooks pass, including mypy, ruff, security, and logging checks.
• The full triggerer test module reached 42 passing tests locally before an existing macOS subprocess test exited with Bad file descriptor; the Linux Core/Other matrix remains delegated to CI.

related: #69841

---

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

• Yes — Codex (GPT-5)

Generated-by: Codex (GPT-5) following the guidelines

[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contributors' Guide
Here are some useful points:

• Pay attention to the quality of your code (ruff, mypy and type annotations). Our prek-hooks will help you with that.
• In case of a new feature add useful documentation (in docstrings or in docs/ directory). Adding a new operator? Check this short guide Consider adding an example Dag that shows how users should use it.
• Consider using Breeze environment for testing locally, it's a heavy docker but it ships with a working Airflow and a lot of integrations.
• Be patient and persistent. It might take some time to get a review or get the final approval from Committers.
• Please follow ASF Code of Conduct for all communication including (but not limited to) comments on Pull Requests, Mailing list and Slack.
• Be sure to read the Airflow Coding style.
• Always keep your Pull Requests rebased, otherwise your build might fail due to changes not related to your commits.
  Apache Airflow is a community-driven project and together we are making it better 🚀.
  In case of doubts contact the developers at:
  Mailing List: dev@airflow.apache.org
  Slack: https://s.apache.org/airflow-slack