DEPR: use DeprecationWarning for Categorical fastpath deprecation
Follow-up on https://github.com/pandas-dev/pandas/pull/52472, changing the warning type. I expect this fastpath to be used in libraries (at least pyarrow did), and first using DeprecationWarning avoids that users see this warning if it's not coming from their own code (i.e. avoids warnings they can't do anything about).
Nice catch, thanks @jorisvandenbossche 