[1.8.x] Fixed #24748 -- Fixed incorrect GROUP BY on MySQL in some queries

When the query's model had a self-referential foreign key, the
compiler.get_group_by() code incorrectly used the self-referential
foreign key's column (for example parent_id) as GROUP BY clause
when it should have used the model's primary key column (id).

Backport of adc57632 from master