Fix TypeError: Use Class Method for load_from_checkpoint (lightning 2.1.1 onwards)

[lauritsf]

• Issue Summary: This pull request addresses a TypeError encountered when calling load_from_checkpoint from an instance of a LightningModule since the update to lightning 2.1.1.
• Technical Details: As outlined in the _restricted_classmethod and load_from_checkpoint implementations, the load_from_checkpoint method must now be called from the class directly.
• Encountered Issue: Additionally, a potential bug involving inspect.getmembers(model) triggering _restricted_class_method in EnsembleLightningModule was identified. This may require further investigation to determine if it necessitates a workaround or a separate issue to be raised with the lightning team.
• Action Requested: Feedback and insights on the _restricted_class_method issue and the overall changes are highly appreciated.

[lauritsf]

I have opened an issue Lightning-AI/pytorch-lightning#19329 with a suggestion that might solve the problem with inspect.getmembers triggering the TypeError

EDIT:
The issue with inspecting class members has been resolved, so I will revisit this when the change becomes part of a new release.