Made BaseConstraint importable from django.db.models.

django/contrib/postgres/constraints.py

@@ -3,8 +3,7 @@ import warnings
 from django.contrib.postgres.indexes import OpClass
 from django.db import NotSupportedError
 from django.db.backends.ddl_references import Expressions, Statement, Table
-from django.db.models import Deferrable, F, Q
-from django.db.models.constraints import BaseConstraint
+from django.db.models import BaseConstraint, Deferrable, F, Q
 from django.db.models.expressions import ExpressionList
 from django.db.models.indexes import IndexExpression
 from django.db.models.sql import Query

django/db/models/constraints.py

@@ -5,7 +5,7 @@ from django.db.models.indexes import IndexExpression
 from django.db.models.query_utils import Q
 from django.db.models.sql.query import Query
 
-__all__ = ["CheckConstraint", "Deferrable", "UniqueConstraint"]
+__all__ = ["BaseConstraint", "CheckConstraint", "Deferrable", "UniqueConstraint"]
 
 
 class BaseConstraint: