DEFAULT NOW() WITH TIME ZONE 'UTC' is getting ignored, thus returning a naive datetime when queried.

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* **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?**: No
* **Python version**: 3.11.1 and 3.10.1
* **Platform**: Windows 11 or PC
* **Do you use pgbouncer?**: No
* **Did you install asyncpg with pip?**: Yes
* **If you built asyncpg locally, which version of Cython did you use?**: No
* **Can the issue be reproduced under both asyncio and
[uvloop](https://github.com/magicstack/uvloop)?**: Probably, never tried.

`DEFAULT NOW() WITH TIME ZONE 'UTC'` is not getting parsed to `datetime.datetime` with `tzinfo`. It basically ignores the `tzinfo` and returns a naive datetime when queried. Inserting an aware datetime is fine though.

Reproduce the report with asyncpg 0.27.0, PostgreSQL 15.1, and Python 3.10 or 3.11 using a DEFAULT NOW() WITH TIME ZONE 'UTC' column. Start by tracing how that returned value is converted to datetime, then verify that the queried result retains tzinfo while aware datetime insertion continues to work.

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