invalid input for query argument (can't subtract offset-naive and offset-aware datetimes)

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* **asyncpg version**: 0.29.0
* **PostgreSQL version**: 13.8
* **Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
the issue with a local PostgreSQL install?**: local postgres 13.8-alpine running in docker
* **Python version**: 3.12.1
* **Platform**: macos
* **Do you use pgbouncer?**: no
* **Did you install asyncpg with pip?**: yes
* **If you built asyncpg locally, which version of Cython did you use?**: N/A
* **Can the issue be reproduced under both asyncio and
[uvloop](https://github.com/magicstack/uvloop)?**: N/A

I'm getting an error:
```shell
File "asyncpg/protocol/prepared_stmt.pyx", line 204, in asyncpg.protocol.protocol.PreparedStatementState._encode_bind_msg
asyncpg.exceptions.DataError: invalid input for query argument $1: datetime.datetime(2024, 3, 21, 21, 17, 9... (can't subtract offset-naive and offset-aware datetimes)
```
When passing python's datetime object with timezone details to be stored in a column without timezone. Minimal steps to reproduce:

```python

import asyncio
import datetime

import asyncpg

DSN = 'postgresql://user:password@host:port/database'

CREATE_SQL = """
DROP TABLE IF EXISTS timestamps_test;
CREATE TABLE timestamps_test
(
ts_no_tz timestamp without time zone,
ts_tz timestamp with time zone
);
"""
INSERT_SQL = "INSERT INTO timestamps_test (ts_no_tz, ts_tz) VALUES ($1, $2);"

async def main():
conn = await asyncpg.connect(DSN)
try:
await conn.execute(CREATE_SQL)
now = datetime.datetime.fromisoformat("2024-03-21 21:17:09.631169+07:00")
await conn.execute(INSERT_SQL, now, now)
finally:
await conn.close()

if __name__ == '__main__':
asyncio.run(main())

```

I understand that timezone details would be lost either way, but it's inconsistent with PostgreSQL's native behaviour, when trying to insert the same date with `psql`:

```psql

$ psql
psql (15.6, server 13.8)
Type "help" for help.

INSERT INTO
timestamps_test (ts_no_tz, ts_tz)
VALUES
(TIMESTAMP '2024-03-21 21:17:09.631169+07:00',
TIMESTAMP WITH TIME ZONE '2024-03-21 21:17:09.631169+07:00');
INSERT 0 1

# SELECT * FROM timestamps_test;
ts_no_tz | ts_tz
----------------------------+-------------------------------
2024-03-21 21:17:09.631169 | 2024-03-21 14:17:09.631169+00
(1 row)
```
timezone info is ignored and lost but there's no error.

Inspect asyncpg/protocol/prepared_stmt.pyx at line 204 and the timestamp argument encoding path; start by running the supplied Python/PostgreSQL reproduction. Done means an aware datetime can be passed to a timestamp without time zone without the offset-mismatch error, while the timestamp with time zone case retains its existing behavior.

Written by the indexing model from the issue text.