Fixed #30158 -- Avoided unnecessary subquery group by on aggregation.

Subquery annotations can be omitted from the GROUP BY clause on aggregation
as long as they are not explicitly grouped against.

Thanks Jonny Fuller for the report.

django/db/models/expressions.py

@@ -1082,6 +1082,11 @@ class Subquery(Expression):
             return clone
         return self
 
+    def get_group_by_cols(self, alias=None):
+        if alias:
+            return [Ref(alias, self)]
+        return []
+
 
 class Exists(Subquery):
     template = 'EXISTS(%(subquery)s)'