Joining workspaces within an overall workspace causes duplicate rooms to appear

[jejb]

Our corporate slack is divided into a load of sub workspaces. Some channels span all workspaces and some are workspace specific. When, as a member of an existing workspace, I join a new workspace with mautrix-slack, all the common channels get duplicated as do all the DMs. The new rooms end up being the ones the bridge sends new messages in the channels and DMs to, so I lose all the history unless I can find the old room (which isn't easy for DMs).