Fix variance issue in _IncEx type alias, only allow True (#1453)

Author: Viicos

python/pydantic_core/_pydantic_core.pyi

@@ -1,4 +1,5 @@
 import datetime
+from collections.abc import Mapping
 from typing import Any, Callable, Generic, Literal, TypeVar, final
 
 from _typeshed import SupportsAllComparisons
@@ -237,7 +238,7 @@ class SchemaValidator:
             `None` if the schema has no default value, otherwise a [`Some`][pydantic_core.Some] containing the default.
         """
 
-_IncEx: TypeAlias = set[int] | set[str] | dict[int, _IncEx | bool] | dict[str, _IncEx | bool]
+_IncEx: TypeAlias = set[int] | set[str] | Mapping[int, _IncEx | Literal[True]] | Mapping[str, _IncEx | Literal[True]]
 
 @final
 class SchemaSerializer: