Database timezone ignored for timestamptz

• asyncpg version: 0.27.0
• PostgreSQL version: 15.1
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: local
• Python version: 3.10.9
• Platform: Linux
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: no
• If you built asyncpg locally, which version of Cython did you use?: 0.29.33
• Can the issue be reproduced under both asyncio and
  uvloop?: not tested, since unlikely

I would expect the datetime.datetime object has the same timezone as psql or python determines (CET).

Instead, asyncpg sets the timezone to UTC.

psql shell, displays UTC+1 = CET properly:

=> select now()::timestamptz;
 2023-02-19 01:53:28.453411+01

python-shell:

>>> loop = asyncio.new_event_loop()
>>> c = loop.run_until_complete(asyncpg.connect(database='lol'))
>>> loop.run_until_complete(c.fetch("select now()::timestamptz"))
[<Record now=datetime.datetime(2023, 2, 19, 0, 54, 39, 597496, tzinfo=datetime.timezone.utc)>]
# ^ here, i'd expect it to be with tzinfo=datetime.timezone(datetime.timedelta(seconds=3600), 'CET')

# because python does the same thing when having timezoned timestamps:
>>> datetime.datetime.now().astimezone()
datetime.datetime(2023, 2, 19, 1, 57, 12, 260030, tzinfo=datetime.timezone(datetime.timedelta(seconds=3600), 'CET'))

Comienza reproduciendo el comportamiento reportado de timestamptz en PostgreSQL 15.1 con asyncpg 0.27.0 y Python 3.10.9 en Linux, comparando la salida de psql con el datetime devuelto. Rastrea la ruta de decodificación del timestamp e identifica las pruebas existentes que cubren valores timestamptz. Se considera terminado cuando el datetime devuelto conserva el comportamiento esperado de la zona horaria local de la base de datos y la regresión está cubierta por una prueba.