Use typing_extensions.Self in the stdlib (#9694)

stdlib/shelve.pyi

@@ -1,8 +1,8 @@
-from _typeshed import Self
 from collections.abc import Iterator, MutableMapping
 from dbm import _TFlags
 from types import TracebackType
 from typing import Any, TypeVar, overload
+from typing_extensions import Self
 
 __all__ = ["Shelf", "BsdDbShelf", "DbfilenameShelf", "open"]
 
@@ -23,7 +23,7 @@ class Shelf(MutableMapping[str, _VT]):
     def __setitem__(self, key: str, value: _VT) -> None: ...
     def __delitem__(self, key: str) -> None: ...
     def __contains__(self, key: str) -> bool: ...  # type: ignore[override]
-    def __enter__(self: Self) -> Self: ...
+    def __enter__(self) -> Self: ...
     def __exit__(
         self, type: type[BaseException] | None, value: BaseException | None, traceback: TracebackType | None
     ) -> None: ...