test: addressing flaky spawn in subprocesses

[Borda]

What does this PR do?

The exception is not properly surfaced from subprocess so the rerun was never used as a check in logs even though the exception was properly linked, since this sample was correctly rerun:

@pytest.mark.flaky(reruns=3, only_rerun="ProcessExitedException")
def test_rerun():
    from torch.multiprocessing import ProcessExitedException
    raise ProcessExitedException("This is a test exception to trigger a rerun.", 0, 0, 0)

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---

📚 Documentation preview 📚: https://pytorch-lightning--20940.org.readthedocs.build/en/20940/

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 pytorch_lightning: Tests workflow

Check ID	Status
pl-cpu-guardian	success	✅

These checks are required after the changes to tests/tests_pytorch/callbacks/test_stochastic_weight_avg.py, tests/tests_pytorch/core/test_results.py.

🟢 pytorch_lightning: Azure GPU

Check ID	Status
pytorch-lightning (GPUs) (testing Lightning | latest)	success	✅
pytorch-lightning (GPUs) (testing PyTorch | latest)	success	✅

These checks are required after the changes to tests/tests_pytorch/callbacks/test_stochastic_weight_avg.py, tests/tests_pytorch/core/test_results.py.

🟢 lightning_fabric: CPU workflow

Check ID	Status
fabric-cpu-guardian	success	✅

These checks are required after the changes to tests/tests_fabric/utilities/test_distributed.py.

🟢 lightning_fabric: Azure GPU

Check ID	Status
lightning-fabric (GPUs) (testing Fabric | latest)	success	✅
lightning-fabric (GPUs) (testing Lightning | latest)	success	✅

These checks are required after the changes to tests/tests_fabric/utilities/test_distributed.py.

---

Thank you for your contribution! 💜

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87%. Comparing base (242d80f) to head (338f7c7).
⚠️ Report is 190 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #20940   +/-   ##
=======================================
- Coverage      87%      87%   -0%     
=======================================
  Files         268      268           
  Lines       23453    23453           
=======================================
- Hits        20404    20401    -3     
- Misses       3049     3052    +3