Add validate_constraints method to the Model stub (#1388)

Author: OvervCW

django-stubs/db/models/base.pyi

@@ -47,6 +47,7 @@ class Model(metaclass=ModelBase):
     def clean_fields(self, exclude: Collection[str] | None = ...) -> None: ...
     def validate_unique(self, exclude: Collection[str] | None = ...) -> None: ...
     def unique_error_message(self, model_class: type[Self], unique_check: Sequence[str]) -> ValidationError: ...
+    def validate_constraints(self, exclude: Collection[str] | None = ...) -> None: ...
     def save(
         self,
         force_insert: bool = ...,