Bug with datetime values in timezone.utc

[ajmarks]

The changes at bee8977 cause a ValueError (at mizani/utils.py:360) when with datetimes using timezone.utc. Repro:

from datetime import datetime, timezone
from mizani.utils import get_timezone

dt = datetime.now(tz=timezone.utc)
get_timezone([dt])

[repnant]

Adding a fuller error message, as this was an extremly frustratingly non-google-able-bug, and it took me way too long too figure out that I needed to demote mizani to 0.8.1 when using plotnine

... mizani/utils.py", line 360, in get_timezone
    raise ValueError(f"Unrecognised timezone class {info.__class__}")
ValueError: Unrecognised timezone class <class 'datetime.timezone'>

[has2k1]

Fix has been released in mizani-0.9.2. Now on pypi and conda.