Add decimal field typings

Author: aleksanb

django-stubs/db/models/fields/__init__.pyi

@@ -1,4 +1,5 @@
 from typing import Any, Optional, Tuple, Iterable, Callable, Dict, Union, Type
+import decimal
 
 from django.db.models import Model
 from django.db.models.query_utils import RegisterLookupMixin
@@ -89,6 +90,7 @@ class DecimalField(IntegerField):
         validators: Iterable[_ValidatorCallable] = ...,
         error_messages: Optional[_ErrorMessagesToOverride] = ...,
     ): ...
+    def __get__(self, instance, owner) -> decimal.Decimal: ...
 
 class AutoField(Field):
     def __get__(self, instance, owner) -> int: ...