### Body

We have several tests marked in the code base with `@pytest.mark.quarantined`
It means that the tests are flaky and if fail in CI it does not fail the build.
The goal is to fix the tests and make them stable.

This task is to gather all of them under the same issue instead of dedicated issue per test.

- [x] [TestImpersonation](https://github.com/apache/airflow/blob/bfcae349b88fd959e32bfacd027a5be976fe2132/tests/core/test_impersonation_tests.py#L117)
- [x] [TestImpersonationWithCustomPythonPath](https://github.com/apache/airflow/blob/bfcae349b88fd959e32bfacd027a5be976fe2132/tests/core/test_impersonation_tests.py#L181)
- [x] [test_exception_propagation](https://github.com/apache/airflow/blob/76f81cd4a7433b7eeddb863b2ae6ee59176cf816/tests/jobs/test_local_task_job.py#L772)
- [x] [test_localtaskjob_maintain_heart_rate](https://github.com/apache/airflow/blob/76f81cd4a7433b7eeddb863b2ae6ee59176cf816/tests/jobs/test_local_task_job.py#L402)
- [x] [test_exception_propagation](https://github.com/apache/airflow/blob/4d0fd8ef6adc35f683c7561f05688a65fd7451f4/tests/executors/test_celery_executor.py#L103)
- [x] [test_process_sigterm_works_with_retries](https://github.com/apache/airflow/blob/65010fda091242870a410c65478eae362899763b/tests/jobs/test_local_task_job.py#L770)


### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.
with create_session() as session:
                pid = (
                    session.query(TaskInstance.pid)
                    .filter(
                        TaskInstance.dag_id == ti.dag_id,
                        TaskInstance.task_id == ti.task_id,
                        TaskInstance.run_id == ti.run_id,
                    )
                    .one_or_none()
                )
                return pid[0]
        def send_signal(ti, signal_sent, sig):
            while True:
                task_pid = get_ti_current_pid(
                    ti
                )  
                if (
                    task_pid and ti.current_state() == State.RUNNING and os.path.isfile(callback_file)
                ):  
                    signal_sent["sent"] = True
                    os.kill(task_pid, sig)
                    break
                time.sleep(1)
        thread = threading.Thread(
            name="signaler",
            target=send_signal,
            args=(ti, signal_sent_status, signal_type),
        )
        thread.daemon = True
        thread.start()