json_agg returns different result for datetime with timezone column

[zulqasar]

Postgres version 15.4

• asyncpg version 0.28.0:
• PostgreSQL version 15.4:
• Python version 3.12:
• macOS Monterey:
• Do you use pgbouncer? NO:
• Did you install asyncpg with pip? YES:
• If you built asyncpg locally, which version of Cython did you use?:
• Can the issue be reproduced under both asyncio and
  uvloop?:

timestamp with timezone column gives different result when used with json_agg function

`

    q = """
    CREATE TABLE IF NOT EXiSTS test_tbl
    (
        id bigint primary key generated by default as identity,
        created_at timestamp with time zone
    )
    """

    async def test():
        async with PG() as pg:
            async with pg.acquire() as con:
    
                # create test_tbl
                await con.execute(q)
    
                # insert data
                now = datetime.now(timezone.utc)
                print('now is: ', now)
                id = await con.fetchval(
                    'Insert into test_tbl (created_at) values ($1) returning id',
                    now
                )
                q1 = "Select created_at from test_tbl where id = $1"
                q2 = f"Select json_agg(e) from ({q1}) e"
    
                r1 = await con.fetchval(q1, id)
                r2 = await con.fetchval(q2, id)
                print('result 1: ', r1)
                print('result 2: ', r2)
    
    asyncio.run(test())

`
RESULTS
now is: 2023-11-15 09:31:22.408820+00:00
result 1: 2023-11-15 09:31:22.408820+00:00
result 2: [{"created_at":"2023-11-15T03:31:22.40882-06:00"}]

row in table
| id | created_at |
| 1 | 2023-11-15 09:31:22.408820 +00:00 |

Executing in postgres
Select json_agg(e) from (select created_at from test_tbl where id = 1) e
Result >>
[{"created_at":"2023-11-15T09:31:22.40882+00:00"}]

[zulqasar]

SET TIME ZONE 'UTC' solved my issue.

Thanks.