Error from array_agg when table has many rows

Hello,

After upgrading from PostgreSQL 12.19 to PostgreSQL 16.3 the function "array_agg" gives me the following error under certain conditions.

ERROR: input of anonymous composite types is not implemented

I was also able reproduce the issue on PostgreSQL 17.4 via the latest currently available Docker image.

Please see the following SQL script for the minimum reproduction.

```
drop table if exists my_table;

create table my_table
(
    my_text text
);

-- Insert a minimum of 200,000 rows.
do
$$
    declare
        counter integer := 0;
    begin
        while counter < 200000
            loop
                INSERT INTO my_table (my_text) VALUES ('A simple sentence.');
                counter := counter + 1;
            end loop;
    end;
$$;

select array_agg(t)
from (select my_text from my_table WHERE my_text != '') t;
```

On my machine the issue appears if 200,000 or more rows exist. I used EXPLAIN and noticed that the query plan is different if this condition is met.

This is the query plan if fewer than 200,000 rows exist.

```
Aggregate  (cost=1935.40..1935.41 rows=1 width=32)
->  Seq Scan on my_table  (cost=0.00..1719.90 rows=86199 width=32)
Filter: (my_text <> ''::text)
```

This is the query plan if more than 200,000 rows exist.

```
Finalize Aggregate  (cost=3801.65..3801.66 rows=1 width=32)
->  Gather  (cost=3801.53..3801.64 rows=1 width=32)
Workers Planned: 1
->  Partial Aggregate  (cost=2801.53..2801.54 rows=1 width=32)
->  Parallel Seq Scan on my_table  (cost=0.00..2548.00 rows=101411 width=32)
Filter: (my_text <> ''::text)
```

I am also able to reproduce the issue on AWS RDS PostgreSQL 16.3.

Thank you!