When a subquery includes a QuerySet, it's impossible to match, because

even though the surrounding Q object attempts to check equality,

QuerySet equality is strictly based on identity.
This change adds a check to see if the value in the Q object is a

QuerySet, and replace it with a subquery placeholder. This changes the

processed WHERE clause from Q(group__in=<QuerySet []>) to

Q(group__in=('__QuerySet__subquery__', 1)), which can be included in

the expected result.

Ran unit tests.
Used in Review Board tests that (under Django 5.2) are including a

QuerySet in the WHERE clause.