Fix ModelCheckpoint.CHECKPOINT_NAME_LAST test interaction

[awaelchli]

What does this PR do?

Fixes a test interaction seen in the master branch. The class attribute is set in one test, and then reset at the end of the test. In case this test fails for some reason, the patched attribute ModelCheckpoint.CHECKPOINT_NAME_LAST would carry over into other tests, causing them to fail since the checkpoint name assertion expects a different "last" name.

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📚 Documentation preview 📚: https://pytorch-lightning--18993.org.readthedocs.build/en/18993/

cc @carmocca @awaelchli @Borda

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 pytorch_lightning: Tests workflow

Check ID	Status
pl-cpu (macOS-11, lightning, 3.8, 1.12, oldest)	success	✅
pl-cpu (macOS-11, lightning, 3.9, 1.12)	success	✅
pl-cpu (macOS-11, lightning, 3.10, 1.13)	success	✅
pl-cpu (macOS-11, lightning, 3.10, 2.0)	success	✅
pl-cpu (macOS-11, lightning, 3.10, 2.1)	success	✅
pl-cpu (ubuntu-20.04, lightning, 3.8, 1.12, oldest)	success	✅
pl-cpu (ubuntu-20.04, lightning, 3.9, 1.12)	success	✅
pl-cpu (ubuntu-20.04, lightning, 3.10, 1.13)	success	✅
pl-cpu (ubuntu-20.04, lightning, 3.10, 2.0)	success	✅
pl-cpu (ubuntu-20.04, lightning, 3.10, 2.1)	success	✅
pl-cpu (windows-2022, lightning, 3.8, 1.12, oldest)	success	✅
pl-cpu (windows-2022, lightning, 3.9, 1.12)	success	✅
pl-cpu (windows-2022, lightning, 3.10, 1.13)	success	✅
pl-cpu (windows-2022, lightning, 3.10, 2.0)	success	✅
pl-cpu (windows-2022, lightning, 3.10, 2.1)	success	✅
pl-cpu (macOS-11, pytorch, 3.8, 1.13)	success	✅
pl-cpu (ubuntu-20.04, pytorch, 3.8, 1.13)	success	✅
pl-cpu (windows-2022, pytorch, 3.8, 1.13)	success	✅
pl-cpu (macOS-12, pytorch, 3.11, 2.0)	success	✅
pl-cpu (macOS-12, pytorch, 3.11, 2.1)	success	✅
pl-cpu (ubuntu-22.04, pytorch, 3.11, 2.0)	success	✅
pl-cpu (ubuntu-22.04, pytorch, 3.11, 2.1)	success	✅
pl-cpu (windows-2022, pytorch, 3.11, 2.0)	success	✅
pl-cpu (windows-2022, pytorch, 3.11, 2.1)	success	✅

These checks are required after the changes to tests/tests_pytorch/checkpointing/test_model_checkpoint.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/checkpointing/test_model_checkpoint.py.

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Thank you for your contribution! 💜

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[codecov]

Codecov Report

Merging #18993 (275e4df) into master (466f772) will decrease coverage by 27%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #18993      +/-   ##
==========================================
- Coverage      76%      48%     -27%     
==========================================
  Files         450      442       -8     
  Lines       36460    36307     -153     
==========================================
- Hits        27563    17507   -10056     
- Misses       8897    18800    +9903