Miscellaneous type_check_only annotations (#13058)

stdlib/dbm/__init__.pyi

@@ -2,7 +2,7 @@ import sys
 from _typeshed import StrOrBytesPath
 from collections.abc import Iterator, MutableMapping
 from types import TracebackType
-from typing import Literal
+from typing import Literal, type_check_only
 from typing_extensions import Self, TypeAlias
 
 __all__ = ["open", "whichdb", "error"]
@@ -89,6 +89,8 @@ class _Database(MutableMapping[_KeyType, bytes]):
         self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None
     ) -> None: ...
 
+# This class is not exposed. It calls itself dbm.error.
+@type_check_only
 class _error(Exception): ...
 
 error: tuple[type[_error], type[OSError]]