sql: insert on conflict fails due to rowid included in star expansion

During star expansion in an insert WHERE clause, the rowid is included which causes the insert to fail unexpectedly.

Repro:
```
create table insertconflicttest(key int4, fruit text);
create unique index plain on insertconflicttest(key);
insert into insertconflicttest as i values (23, 'Jackfruit') on conflict (key) do update set fruit = excluded.fruit where i.* != excluded.* returning *;
```

This is successful in postgres, but CRDB returns an error:
```
ERROR: expected tuple ((key, fruit, rowid) AS key, fruit, rowid) to have a length of 2
```

Relatedly, sometimes the rowid is also incorrectly exposed, such as in the following example:
```
insert into insertconflicttest as i values (23, 'Avocado') on conflict (key) do update set fruit = excluded.*::text returning *;
-- CRDB: 23 | (23,Avocado,933152993262665729)
-- postgres: 23 | (23,Avocado)
```

Found in pg_regress insert_conflict.sql

Jira issue: CRDB-35261