TST: correct parquet test expected partition column dtype for pyarrow 2.0
Follow-up on https://github.com/pandas-dev/pandas/pull/35814, but now incorporating the changes in pyarrow 2.0

cc @alimcmaster1 

Also related to https://github.com/pandas-dev/pandas/issues/37286 and https://github.com/pandas-dev/pandas/pull/37296/ (timezone related failures), but doing this fix separate as it's not something that needs to be reverted.
