Check copies blackify
# What does this PR do?

This PR update the check_copies utils to apply black when checking if a copy has diverged from the original when replacement happen. An example of the problem is given with the diff in `modeling_mobilebert.py` here, where the check copies could not be applied to whole class because of styling divergences.

It also fixes a bug where the check was not applied on functions after the end of the definition (it wasn't checking the function but was stopping at the first unindent when the closing parenthesis was). As a consequence, three files are changed because they diverged from the original function:
- modeling_m2m_100.py
- modeling_roberta.py
- modeling_speech_to_text.py

I'm not sure if the check should be removed on those or not (cc @patil-suraj )