Fix Quarantine tests

[eladkal]

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.

• TestImpersonation
• TestImpersonationWithCustomPythonPath
• test_exception_propagation
• test_localtaskjob_maintain_heart_rate
• test_exception_propagation
• test_process_sigterm_works_with_retries

Committer

• I acknowledge that I am a maintainer/committer of the Apache Airflow project.

[Taragolis]

TestImpersonation, TestImpersonationWithCustomPythonPath and test_exception_propagation might fix by #28378 - it is still quarantined but at least it should not failed

[potiuk]

I thnk this one is the last: test_process_sigterm_works_with_retries

[Taragolis]

#29075 😢 😞