Fixed regressions from 36ded015.

Refs #21302

django/contrib/gis/db/models/sql/aggregates.py

-from django.db.models.sql.aggregates import Aggregate, Count
+from django.db.models.sql import aggregates
+from django.db.models.sql.aggregates import *  # NOQA
 from django.contrib.gis.db.models.fields import GeometryField
 
 
-__all__ = ['Count', 'Collect', 'Extent', 'Extent3D', 'MakeLine', 'Union']
+__all__ = ['Collect', 'Extent', 'Extent3D', 'MakeLine', 'Union'] + aggregates.__all__
 
 
 class GeoAggregate(Aggregate):

django/db/models/sql/aggregates.py

@@ -5,6 +5,10 @@ import copy
 
 from django.db.models.fields import IntegerField, FloatField
 
+
+__all__ = ['Aggregate', 'Avg', 'Count', 'Max', 'Min', 'StdDev', 'Sum', 'Variance']
+
+
 # Fake fields used to identify aggregate types in data-conversion operations.
 ordinal_aggregate_field = IntegerField()
 computed_aggregate_field = FloatField()