Log Message:
Update chat/matrix-synapse to 1.91.2

# Synapse 1.91.2 (2023-09-06)

### Bugfixes

- Revert \ 
[MSC3861](https://github.com/matrix-org/matrix-spec-proposals/pull/3861) \ 
introspection cache, admin impersonation and account lock. \ 
([\#16258](https://github.com/matrix-org/synapse/issues/16258))

# Synapse 1.91.1 (2023-09-04)

### Bugfixes

- Fix a performance regression introduced in Synapse 1.91.0 where event \ 
persistence would cause an excessive linear growth in CPU usage. \ 
([\#16220](https://github.com/matrix-org/synapse/issues/16220))