Fix save_last type annotation for ModelCheckpoint

[mariovas3]

What does this PR do?

Fixes #19799

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  • yes
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  • no breaking changes in this PR
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📚 Documentation preview 📚: https://pytorch-lightning--19808.org.readthedocs.build/en/19808/

[mariovas3]

The PR is pretty compact - few modifications in 2 files.

The PR has been ready to review for the last 3 weeks. It passes all available tests.

Please someone review it, so I can close the issue and the PR.

[awaelchli]

@mariovas3 That's a great fix, thanks for sending the PR and including a test as well!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53%. Comparing base (1a6786d) to head (f165de2).
Report is 97 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (1a6786d) and HEAD (f165de2). Click for more details.

HEAD has 272 uploads less than BASE

Flag	BASE (1a6786d)	HEAD (f165de2)
python3.10	23	11
cpu	91	23
lightning	55	15
pytest	71	2
examples	9	0
app	9	0
lightning_fabric	19	0
python3.11	34	6
gpu	4	2
python3.8	18	6
pytest-full	24	23
pytorch2.3	3	2
lightning_app	2	0

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #19808      +/-   ##
==========================================
- Coverage      84%      53%     -31%     
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  Files         426      418       -8     
  Lines       35264    35111     -153     
==========================================
- Hits        29553    18703   -10850     
- Misses       5711    16408   +10697