Use dbm._TFlags in shelve.open (#7084)

stdlib/shelve.pyi

@@ -1,5 +1,6 @@
 from _typeshed import Self
 from collections.abc import Iterator, MutableMapping
+from dbm import _TFlags
 from types import TracebackType
 from typing import TypeVar, overload
 
@@ -34,6 +35,6 @@ class BsdDbShelf(Shelf[_VT]):
     def last(self) -> tuple[str, _VT]: ...
 
 class DbfilenameShelf(Shelf[_VT]):
-    def __init__(self, filename: str, flag: str = ..., protocol: int | None = ..., writeback: bool = ...) -> None: ...
+    def __init__(self, filename: str, flag: _TFlags = ..., protocol: int | None = ..., writeback: bool = ...) -> None: ...
 
-def open(filename: str, flag: str = ..., protocol: int | None = ..., writeback: bool = ...) -> Shelf[object]: ...
+def open(filename: str, flag: _TFlags = ..., protocol: int | None = ..., writeback: bool = ...) -> Shelf[object]: ...