Fix django.contrib.admin.options.BaseModelAdmin.has_add_permission (#205)

* Fix `django.contrib.admin.options.BaseModelAdmin.has_add_permission` (#203).

* Add `django.db.models.base.Model.unique_error_message` (#204).

django-stubs/contrib/admin/options.pyi

@@ -86,7 +86,7 @@ class BaseModelAdmin:
     def get_sortable_by(self, request: HttpRequest) -> Union[List[Callable], List[str], Tuple]: ...
     def lookup_allowed(self, lookup: str, value: str) -> bool: ...
     def to_field_allowed(self, request: HttpRequest, to_field: str) -> bool: ...
-    def has_add_permission(self, request: HttpRequest, obj: Optional[Model] = ...) -> bool: ...
+    def has_add_permission(self, request: HttpRequest) -> bool: ...
     def has_change_permission(self, request: HttpRequest, obj: Optional[Model] = ...) -> bool: ...
     def has_delete_permission(self, request: HttpRequest, obj: Optional[Model] = ...) -> bool: ...
     def has_view_permission(self, request: HttpRequest, obj: Optional[Model] = ...) -> bool: ...

django-stubs/db/models/base.pyi

@@ -1,6 +1,7 @@
-from typing import Any, Dict, List, Optional, Sequence, Set, Tuple, TypeVar, Union, Collection
+from typing import Any, Callable, Dict, List, Optional, Sequence, Set, Tuple, Type, TypeVar, Union, Collection
 
 from django.core.checks.messages import CheckMessage
+from django.core.exceptions import ValidationError
 from django.db.models.manager import Manager
 from django.db.models.options import Options
 
@@ -22,6 +23,9 @@ class Model(metaclass=ModelBase):
     def clean(self) -> None: ...
     def clean_fields(self, exclude: Optional[Collection[str]] = ...) -> None: ...
     def validate_unique(self, exclude: Optional[Collection[str]] = ...) -> None: ...
+    def unique_error_message(
+        self, model_class: Type[_Self], unique_check: Collection[Union[Callable, str]]
+    ) -> ValidationError: ...
     def save(
         self,
         force_insert: bool = ...,