The algorithm failed to find the correct category by slug when there are multiple sub-sub-categories with the same child-category name and the first child doesn't have the correct grandchild.
So, searching for "child / grandchild" worked in the following case, it found (3):
- (1) parent 1
- (2) child
- (3) grandchild
- (4) parent 2
- (5) child
- (6) grandchild
But it failed to find the grandchild in the following case:
- (1) parent 1
- (2) child
- (4) parent 2
- (5) child
- (6) grandchild
And this also fixes a flaky spec by forcing categories to always order by by `parent_category_id` and `id`.
This makes it possible to partly revert 60990aab55
e17c145e8d