fix(matrix): use correct reply_to_message_id parameter name

Fixes #1842

The MessageEvent dataclass expects 'reply_to_message_id' but the Matrix
connector was passing 'reply_to'. This caused replies to fail with:

    MessageEvent.__init__() got an unexpected keyword argument 'reply_to'

Changed the parameter name to match the dataclass definition.

gateway/platforms/matrix.py

@@ -635,7 +635,7 @@ class MatrixAdapter(BasePlatformAdapter):
             source=source,
             raw_message=getattr(event, "source", {}),
             message_id=event.event_id,
-            reply_to=reply_to,
+            reply_to_message_id=reply_to,
         )
 
         await self.handle_message(msg_event)