cannot run test suite in python3.12 due to warnings filter

[jeromedockes]

in the pyproject.toml we configure pytest to transform deprecation warnings into errors.
in python3.12 simply importing pandas produces a deprecation warning

import warnings
warnings.filterwarnings("error")
import pandas

shows

DeprecationWarning: datetime.datetime.utcfromtimestamp() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.fromtimestamp(timestamp, datetime.UTC).

I'll open a PR ignoring that warning (it's in pandas so there's not much we can do about it except report it) and addding a python3.12 build