Skip keys not in the state dict when finding mismatched weights
# What does this PR do?

When looping through the keys in `find_mismatched_weights`, we loop through all the `loaded_keys` which are all the keys in the checkpoint. If the checkpoint is sharded, the `state_dict` passed won't contain all those keys, only a subset of them, so we need to skip the keys not present in the `state_dict`.

Fixes #24704 
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