Add some missing Self return annotations in redis (#9601)

Author: wookie184

stubs/redis/redis/asyncio/client.pyi

@@ -116,7 +116,7 @@ class Monitor:
     connection: Any
     def __init__(self, connection_pool: ConnectionPool) -> None: ...
     async def connect(self) -> None: ...
-    async def __aenter__(self): ...
+    async def __aenter__(self: Self) -> Self: ...
     async def __aexit__(self, *args) -> None: ...
     async def next_command(self) -> MonitorCommandInfo: ...
     def listen(self) -> AsyncIterator[MonitorCommandInfo]: ...
@@ -142,7 +142,7 @@ class PubSub:
         ignore_subscribe_messages: bool = ...,
         encoder: Incomplete | None = ...,
     ) -> None: ...
-    async def __aenter__(self): ...
+    async def __aenter__(self: Self) -> Self: ...
     async def __aexit__(self, exc_type, exc_value, traceback) -> None: ...
     def __del__(self) -> None: ...
     async def reset(self) -> None: ...