make ValuesQuerySet have proper Collection generic type (#140)

django-stubs/forms/models.pyi

@@ -6,7 +6,7 @@ from uuid import UUID
 from django.core.files.base import File
 from django.db.models.base import Model
 from django.db.models.manager import Manager
-from django.db.models.query import QuerySet
+from django.db.models.query import QuerySet, _BaseQuerySet
 from django.db.models.query_utils import Q
 from django.forms.fields import CharField, ChoiceField, Field
 from django.forms.forms import BaseForm, DeclarativeFieldsMetaclass
@@ -262,7 +262,7 @@ class ModelMultipleChoiceField(ModelChoiceField):
     widget: Any = ...
     hidden_widget: Any = ...
     default_error_messages: Any = ...
-    def __init__(self, queryset: QuerySet, **kwargs: Any) -> None: ...
+    def __init__(self, queryset: _BaseQuerySet, **kwargs: Any) -> None: ...
 
 def _get_foreign_key(
     parent_model: Type[Model], model: Type[Model], fk_name: Optional[str] = ..., can_fail: bool = ...