Fix LightningCLI loading of hyperparameters from ckpt_path failing for subclass model mode

[mauvilsa]

What does this PR do?

Fixes torchgeo/torchgeo#2995
Maybe also fixes mehta-lab/VisCy#291

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📚 Documentation preview 📚: https://pytorch-lightning--21246.org.readthedocs.build/en/21246/