Add Session annotation for sessionmaker call (#8257)

stubs/SQLAlchemy/sqlalchemy/orm/session.pyi

@@ -214,7 +214,7 @@ class sessionmaker(_SessionClassMethods):
         **kw,
     ) -> None: ...
     def begin(self): ...
-    def __call__(self, **local_kw): ...
+    def __call__(self, **local_kw) -> Session: ...
     def configure(self, **new_kw) -> None: ...
 
 def close_all_sessions() -> None: ...