Bump sync protocol version to 9 to indicate client reset fix

[sync-by-unito]

Since the client reset failure during async open task (RCORE-1614) has been fixed, bump the protocol version to 9 to inform the server that the client has integrated this fix.

The server is also going to be updated (BAAS-21624) for clients still using protocol version 8 to send the schema instructions via a "fake" PBS download message when a client first connects to the server after it has been migrated to FLX, which will initialize an empty realm with the server schema to avoid seeing the client reset failure.