Adding test for legacy checkpoint created with 2.5.1

[pl-ghost]

This is automated addition of created checkpoints with the latest lightning release!

cc @lantiga @Borda

[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/legacy/back-compatible-versions.txt.

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Thank you for your contribution! 💜

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79%. Comparing base (5cbfb86) to head (35e607c).
Report is 120 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (5cbfb86) and HEAD (35e607c). Click for more details.

HEAD has 606 uploads less than BASE

Flag	BASE (5cbfb86)	HEAD (35e607c)
gpu	4	0
pytest	85	0
lightning	91	15
lightning_fabric	39	0
cpu	162	27
python	18	3
python3.10	36	6
python3.11	36	6
python3.12.7	54	9
python3.12	18	3
pytorch2.1	18	6
pytorch_lightning	36	12
pytest-full	81	27
pytorch2.2.2	9	3
pytorch2.5	9	3
pytorch2.3	9	3
pytorch2.4.1	9	3
pytorch2.7	9	3
pytorch2.5.1	9	3
pytorch2.6	9	3

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #20659     +/-   ##
=========================================
- Coverage      87%      79%     -9%     
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  Files         268      265      -3     
  Lines       23449    23394     -55     
=========================================
- Hits        20501    18386   -2115     
- Misses       2948     5008   +2060