check param is of nn.Parameter type for pruning sanitization

[chanokin]

Pruning breaks because of non-Parameter types being passed through the pipeline. This came up for an LSTM module, the bias parameter is a boolean which breaks later stages of the pruning.

What does this PR do?

I've only added a further check for the type of "prunable parameters" in the sanitize_parameters_to_prune function. I check if the parameter is of type nn.Parameter so it has the to method and device property.

Fixes #10835

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📚 Documentation preview 📚: https://pytorch-lightning--20783.org.readthedocs.build/en/20783/

[rittik9]

This looks good to me, can we also add a test for this??