Check copies match full class/function names
# What does this PR do?

@LysandreJik pointed out a failure in the `check_copies` script that came from the fact that when looking for the code of an object, the script was matching the first line it found that begun with the name of the object. So it would match `DebertaLayer` with `DebertaLayerNorm` and compare those.

This PR fixes that.