opt: missing ambiguous column error with an aliased join

**Describe the problem**

When an aliased join has multiple columns with the same name, it is possible to reference that name without getting an ambiguous column error.

**To Reproduce**

On `master` (23.2 beta), run `cockroach demo`. Then run:
```
CREATE TABLE t (a INT PRIMARY KEY, b INT);
CREATE TABLE u (a INT PRIMARY KEY, c INT);
SELECT * FROM t LEFT JOIN (SELECT * FROM t JOIN u ON b = c) j ON j.a = t.a;
```

This succeeds on CockroachDB, but fails on Postgres with the error:
```
ERROR: column reference "a" is ambiguous
LINE 1: ... LEFT JOIN (SELECT * FROM t JOIN u ON b = c) j ON j.a = t.a;
^
```

**Expected behavior**

CockroachDB should match Postgres behavior and return an error in this case.

Jira issue: CRDB-34167