Fix trainer.fit docstring render bug

[ritoban23]

What does this PR do?

Fixes a documentation rendering bug in trainer.fit where :rtype: None was incorrectly displayed.
The fix wraps the "For more information about multiple dataloaders" text in a proper RST .. note:: directive, ensuring correct Sphinx formatting and preventing spurious :rtype: output.

Fixes #21356

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---

📚 Documentation preview 📚: https://pytorch-lightning--21362.org.readthedocs.build/en/21362/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79%. Comparing base (b15d394) to head (a4315bf).
✅ All tests successful. No failed tests found.

❗ There is a different number of reports uploaded between BASE (b15d394) and HEAD (a4315bf). Click for more details.

HEAD has 1053 uploads less than BASE

Flag	BASE (b15d394)	HEAD (a4315bf)
cpu	264	27
python3.10	59	6
lightning_fabric	58	0
pytest	132	0
lightning	146	15
python3.12.7	89	9
python3.11	58	6
python3.12	29	3
python	29	3
pytorch2.2.2	14	3
pytest-full	132	27
pytorch2.1	29	6
pytorch_lightning	60	12
pytorch2.5.1	15	3
pytorch2.7	15	3
pytorch2.4.1	15	3
pytorch2.6	15	3
pytorch2.8	15	3
pytorch2.3	14	3

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #21362     +/-   ##
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- Coverage      87%      79%     -8%     
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  Files         269      266      -3     
  Lines       23744    23689     -55     
=========================================
- Hits        20572    18671   -1901     
- Misses       3172     5018   +1846     

[deependujha]

Hi @ritoban23, thanks for choosing to make PyTorch Lightning more awesome. Can you please look at failing doc tests?

[turbotimon]

I'm wondering why the note is necessary and why it is not the same issue e.g. here:

pytorch-lightning/src/lightning/pytorch/trainer/trainer.py

Line 924 in a4315bf

See :ref:`Lightning inference section<deploy/production_basic:Predict step with your LightningModule>` for more.

However, it may would fix the problem and be more concise to just move the "For more.." sentence up, just below the parameters, like it is done in validate, test and predict:

pytorch-lightning/src/lightning/pytorch/trainer/trainer.py

Lines 663 to 677 in a4315bf

	weights_only: Defaults to ``None``. If ``True``, restricts loading to ``state_dicts`` of plain
	``torch.Tensor`` and other primitive types. If loading a checkpoint from a trusted source that contains
	an ``nn.Module``, use ``weights_only=False``. If loading checkpoint from an untrusted source, we
	recommend using ``weights_only=True``. For more information, please refer to the
	`PyTorch Developer Notes on Serialization Semantics <https://docs.pytorch.org/docs/main/notes/serialization.html#id3>`_.
	For more information about multiple dataloaders, see this :ref:`section <multiple-dataloaders>`.
	Returns:
	List of dictionaries with metrics logged during the validation phase, e.g., in model- or callback hooks
	like :meth:`~lightning.pytorch.LightningModule.validation_step` etc.
	The length of the list corresponds to the number of validation dataloaders used.
	Raises:
	TypeError: