We must not process incoming updates for a given channel until we ~finished reestablishing it.
Consider both parties have some unacked updates they want to replay during reestablish.
If Bob reacts to Alice's replayed stuff before he himself replays his stuff, madness ensues.
I think this should fix the remaining part of https://github.com/spesmilo/electrum/pull/8778
(timing issues when running the unit tests with py3.12)
79d88dcb5f