fix(providers/standard): improve error message for non-serializable op_kwargs in virtualenv operators

[YoannAbriel]

Problem

When render_template_as_native_obj=True on a DAG, templates like {{ ti }} in op_kwargs resolve to live TaskInstance objects instead of strings. When PythonVirtualenvOperator._write_args tries to pickle these for the subprocess, it fails with a PicklingError from structlog internals (Only BytesLoggers to sys.stdout and sys.stderr can be pickled). The error gives no indication that the root cause is a non-serializable kwarg value.

Root Cause

_write_args calls self.pickling_library.dumps(...) on the full args dict without any pre-validation. When a value can't be pickled, the raw exception propagates — and since TaskInstance contains structlog loggers, the error message references structlog internals rather than the actual problem.

Fix

Wrap the dumps call in a try/except. On failure, iterate over op_kwargs to identify which specific keys hold non-serializable values, then raise an AirflowException naming the bad keys and suggesting alternatives (e.g. {{ ti.task_id }} instead of {{ ti }}).

Added a unit test that verifies the improved error message when a non-serializable object is passed in op_kwargs.

Closes: #61741

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

• Yes — Claude Code

Generated-by: Claude Code following the guidelines

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[potiuk]

@YoannAbriel This PR has been converted to draft because it does not yet meet our Pull Request quality criteria.

Issues found:

• ❌ Pre-commit / static checks: Failing: CI image checks / Static checks. Run prek run --from-ref main locally to find and fix issues. See Pre-commit / static checks docs.
• ❌ mypy (type checking): Failing: CI image checks / MyPy checks (mypy-airflow-core). Run prek --stage manual mypy-airflow-core --all-files locally to reproduce. You need breeze ci-image build --python 3.10 for Docker-based mypy. See mypy (type checking) docs.
• ❌ Provider tests: Failing: Postgres tests: providers / DB-prov:Postgres:14:3.10:-amazon,celer...standard, MySQL tests: providers / DB-prov:MySQL:8.0:3.10:-amazon,celer...standard, Sqlite tests: providers / DB-prov:Sqlite:3.10:-amazon,celer...standard, Non-DB tests: providers / Non-DB-prov::3.10:-amazon,celer...standard, Special tests / Min SQLAlchemy test: providers / DB-prov:MinSQLAlchemy-Postgres:14:3.10:-amazon,celer...standard (+6 more). Run provider tests with breeze run pytest <provider-test-path> -xvs. See Provider tests docs.
• ❌ Other failing CI checks: Failing: CI image checks / Test Python API client, Postgres tests: core / DB-core:Postgres:14:3.10:API...Serialization, MySQL tests: core / DB-core:MySQL:8.0:3.10:API...Serialization, Sqlite tests: core / DB-core:Sqlite:3.10:API...Serialization, Non-DB tests: core / Non-DB-core::3.10:API...Serialization (+8 more). Run prek run --from-ref main locally to reproduce. See static checks docs.

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