fix(providers/standard): improve error message for non-serializable op_kwargs in PythonVirtualenvOperator (#63270)

When render_template_as_native_obj=True, templates like {{ ti }} resolve to
live Airflow objects that can't be pickled. The resulting PicklingError from
structlog internals is confusing and doesn't point to the root cause.

Catch serialization failures in _write_args, identify which specific kwargs
failed, and raise a clear AirflowException naming the bad keys and suggesting
to use string attributes instead.

Closes: #61741