run_command_on_colocated_placements does not work on reference tables

```sql
-- Repro code
CREATE TABLE reference_a (
id int PRIMARY KEY,
val int
);
CREATE TABLE reference_b (
id int PRIMARY KEY,
val int
);
SELECT create_reference_table('reference_a');
SELECT create_reference_table('reference_b');
INSERT INTO reference_a (id, val) VALUES (1, 1);
INSERT INTO reference_b (id, val) VALUES (1, 2);

SELECT run_command_on_colocated_placements(
'reference_a',
'reference_b',
$cmd$SELECT a.val + b.val combined FROM reference_a a join reference_b b on a.id = b.id$cmd$
);
```
The code seems to expect distributed tables only. Is there a way to do something similar with reference tables?

I am trying to create a reference table which has an audit trigger to put a copy in a reference history table.

Thanks, John

Start by running the SQL reproduction using run_command_on_colocated_placements with reference_a and reference_b. Read the behavior around reference tables and the function's handling of distributed tables, then determine whether equivalent execution or a documented limitation is expected. Done means the reference-table audit/history use case has a clear supported outcome.

Written by the indexing model from the issue text.