Adding test for legacy checkpoint created with 2.5.1.post0

[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 (69d8fa9) to head (260a865).
⚠️ Report is 123 commits behind head on master.
✅ All tests successful. No failed tests found.

❗ There is a different number of reports uploaded between BASE (69d8fa9) and HEAD (260a865). Click for more details.

HEAD has 836 uploads less than BASE

Flag	BASE (69d8fa9)	HEAD (260a865)
cpu	214	27
python	24	3
lightning_fabric	50	0
pytest	111	0
python3.10	47	6
python3.12	24	3
lightning	120	15
python3.12.7	72	9
python3.11	47	6
gpu	3	0
pytorch2.1	24	6
pytorch_lightning	47	12
pytest-full	106	27
pytorch2.3	12	3
pytorch2.5	11	3
pytorch2.2.2	11	3
pytorch2.7	12	3
pytorch2.4.1	12	3
pytorch2.6	12	3
pytorch2.5.1	12	3

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #20756     +/-   ##
=========================================
- Coverage      87%      79%     -8%     
=========================================
  Files         268      265      -3     
  Lines       23452    23397     -55     
=========================================
- Hits        20388    18389   -1999     
- Misses       3064     5008   +1944     

[Borda]

not needed