Fix incorrect serialisation of the FixedTimezone

[millin]

When the start_date of a DAG is specified with a fixed timezone, its serialisation will not be correct and this causes the scheduler to crash.

Example of an entry in the data column of the table serialized_dag
before fix:

{
...
  "start_date": 1684684800.0,
  "timezone": "FixedTimezone(28800, name=\"+08:00\")",
...
}

after fix:

{
...
  "start_date": 1684684800.0,
  "timezone": 28800,
...
}

Crash log

Traceback (most recent call last):
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/cli/commands/scheduler_command.py", line 52, in _run_scheduler_job
    run_job(job=job_runner.job, execute_callable=job_runner._execute)
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/utils/session.py", line 79, in wrapper
    return func(*args, session=session, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/jobs/job.py", line 393, in run_job
    return execute_job(job, execute_callable=execute_callable)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/jobs/job.py", line 422, in execute_job
    ret = execute_callable()
          ^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/jobs/scheduler_job_runner.py", line 855, in _execute
    self._run_scheduler_loop()
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/jobs/scheduler_job_runner.py", line 987, in _run_scheduler_loop
    num_queued_tis = self._do_scheduling(session)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/jobs/scheduler_job_runner.py", line 1061, in _do_scheduling
    self._create_dagruns_for_dags(guard, session)
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/utils/retries.py", line 91, in wrapped_function
    for attempt in run_with_db_retries(max_retries=retries, logger=logger, **retry_kwargs):
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/tenacity/__init__.py", line 347, in __iter__
    do = self.iter(retry_state=retry_state)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/tenacity/__init__.py", line 314, in iter
    return fut.result()
           ^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/concurrent/futures/_base.py", line 449, in result
    return self.__get_result()
           ^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/concurrent/futures/_base.py", line 401, in __get_result
    raise self._exception
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/utils/retries.py", line 100, in wrapped_function
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/jobs/scheduler_job_runner.py", line 1133, in _create_dagruns_for_dags
    self._create_dag_runs(non_dataset_dags, session)
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/jobs/scheduler_job_runner.py", line 1167, in _create_dag_runs
    dag = self.dagbag.get_dag(dag_model.dag_id, session=session)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/utils/session.py", line 76, in wrapper
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/models/dagbag.py", line 191, in get_dag
    self._add_dag_from_db(dag_id=dag_id, session=session)
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/models/dagbag.py", line 273, in _add_dag_from_db
    dag = row.dag
          ^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/models/serialized_dag.py", line 231, in dag
    return SerializedDAG.from_dict(data)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/serialization/serialized_objects.py", line 1443, in from_dict
    return cls.deserialize_dag(serialized_obj["dag"])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/serialization/serialized_objects.py", line 1362, in deserialize_dag
    v = cls._deserialize_timezone(v)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/airflow/utils/timezone.py", line 294, in parse_timezone
    return pendulum.timezone(name)  # type: ignore[operator]
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/pendulum/__init__.py", line 86, in timezone
    return Timezone(name)
           ^^^^^^^^^^^^^^
  File "/usr/local/airflow/.local/lib/python3.11/site-packages/pendulum/tz/timezone.py", line 67, in __new__
    raise InvalidTimezone(key)
pendulum.tz.exceptions.InvalidTimezone: FixedTimezone(28800, name="+08:00")
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/zoneinfo/_common.py", line 12, in load_tzdata
    return resources.files(package_name).joinpath(resource_name).open("rb")
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/pathlib.py", line 1044, in open
    return io.open(self, mode, buffering, encoding, errors, newline)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: '/usr/local/airflow/.local/lib/python3.11/site-packages/tzdata/zoneinfo/FixedTimezone(28800, name="+08:00")'

This issue introduced in Airflow 2.8.

---

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[uranusjr]

I hate Pendulum’s timezone classes

[potiuk]

I hate Pendulum’s timezone classes

You are not alone

[Taragolis]

I expect that this happen only in Pendulum 3 because inheritance of pendulum timezones changed in that version.

Let's me join to the club who hate pendulum timezones😅

[millin]

Maybe this fix should be cherry-picked to the 2.8.4 version?