Fix race condition in Fabric test

[awaelchli]

What does this PR do?

There is a race condition if we do these in a sequence:

torch.distributed.destroy_process_group()
torch.distributed.init_process_group()

If one of the processes is slightly faster, and enters the init call before the other one finished destruction, we get in trouble.

cc @carmocca @akihironitta @Borda

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 lightning_fabric: CPU workflow

Check ID	Status
fabric-cpu (macOS-11, lightning, 3.8, 1.11)	success	✅
fabric-cpu (macOS-11, lightning, 3.9, 1.12)	success	✅
fabric-cpu (macOS-11, lightning, 3.10, 1.13)	success	✅
fabric-cpu (macOS-11, lightning, 3.8, 1.11, oldest)	success	✅
fabric-cpu (macOS-11, lightning, 3.9, 2.0, pre)	success	✅
fabric-cpu (ubuntu-20.04, lightning, 3.9, 1.11)	success	✅
fabric-cpu (ubuntu-20.04, lightning, 3.10, 1.12)	success	✅
fabric-cpu (ubuntu-20.04, lightning, 3.10, 1.13)	success	✅
fabric-cpu (ubuntu-20.04, lightning, 3.8, 1.11, oldest)	success	✅
fabric-cpu (ubuntu-20.04, lightning, 3.9, 2.0, pre)	success	✅
fabric-cpu (windows-2022, lightning, 3.9, 1.11)	success	✅
fabric-cpu (windows-2022, lightning, 3.10, 1.12)	success	✅
fabric-cpu (windows-2022, lightning, 3.10, 1.13)	success	✅
fabric-cpu (windows-2022, lightning, 3.8, 1.11, oldest)	success	✅
fabric-cpu (windows-2022, lightning, 3.9, 2.0, pre)	success	✅
fabric-cpu (macOS-11, fabric, 3.8, 1.13)	success	✅
fabric-cpu (ubuntu-20.04, fabric, 3.8, 1.13)	success	✅
fabric-cpu (windows-2022, fabric, 3.8, 1.13)	success	✅

These checks are required after the changes to tests/tests_fabric/parity/test_parity_ddp.py.

🟢 lightning_fabric: Azure GPU

Check ID	Status
lightning-fabric (GPUs)	success	✅

These checks are required after the changes to tests/tests_fabric/parity/test_parity_ddp.py.

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Thank you for your contribution! 💜

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