Fixed #34024 -- Fixed crash when aggregating querysets with Q objects annotations.

This reverts b64db05b9cedd96905d637a2d824cbbf428e40e7.

It was reasonable to assume it was unnecessary code as there were
no failing tests upon its removal. This commit adds the necessary
regression tests for the failing condition identified in #34024
alongside the original tests added in the PR for which
WhereNode.is_summary was introduced.

django/db/models/sql/where.py

@@ -244,6 +244,10 @@ class WhereNode(tree.Node):
     def contains_over_clause(self):
         return self._contains_over_clause(self)
 
+    @property
+    def is_summary(self):
+        return any(child.is_summary for child in self.children)
+
     @staticmethod
     def _resolve_leaf(expr, query, *args, **kwargs):
         if hasattr(expr, "resolve_expression"):

tests/aggregation_regress/tests.py

@@ -554,6 +554,9 @@ class AggregationTests(TestCase):
             325,
         )
 
+    def test_q_annotation_aggregate(self):
+        self.assertEqual(Book.objects.annotate(has_pk=Q(pk__isnull=False)).count(), 6)
+
     def test_decimal_aggregate_annotation_filter(self):
         """
         Filtering on an aggregate annotation with Decimal values should work.