Timezone information is stripped from metadata validity timestamp

[nmeheus]

Within the ServiceProvider model, the timezone information is stripped from the metadata_expiration_dt field on multiple occasions. This causes errors when comparing to timezone aware datetimes. Ideally the meta attribute is used as is, given that it should be using a timezone aware datetime format.

[fmors]

I'm facing a similar issue after moving my project to Python 3.12. I see this package uses pytz and utcnow() in some instances, which were deprecated on more recent Python versions.