Use _typeshed.Self with __enter__ (#5723)

Co-authored-by: Sebastian Rittau <srittau@rittau.biz>
Co-authored-by: Akuli <akuviljanen17@gmail.com>

stdlib/sqlite3/dbapi2.pyi

@@ -1,5 +1,5 @@
 import sys
-from _typeshed import StrOrBytesPath
+from _typeshed import Self, StrOrBytesPath
 from datetime import date, datetime, time
 from typing import Any, Callable, Generator, Iterable, Iterator, List, Optional, Protocol, Tuple, Type, TypeVar, Union
 
@@ -158,7 +158,7 @@ class Connection(object):
             sleep: float = ...,
         ) -> None: ...
     def __call__(self, *args: Any, **kwargs: Any) -> Any: ...
-    def __enter__(self) -> Connection: ...
+    def __enter__(self: Self) -> Self: ...
     def __exit__(self, t: Optional[type], exc: Optional[BaseException], tb: Optional[Any]) -> None: ...
 
 class Cursor(Iterator[Any]):