Adding a room ACL that denies a server does not prevent typing notifications

This issue has been migrated from [#11456](https://github.com/matrix-org/synapse/issues/11456).

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### Description

Hi, I have a user who hosts his own dendrite server who I have banned from a room. He however has been sending typing notifications to my room for the last 13 hours to annoy my users. I have tried sending an acl that denies his server from communicating, but that has not prevented his typing notifications.

Unfortunately, I do not know how he has been sending these typing notifications.

I would expect sending a room acl to deny a server would prevent users from sending typing notifications.

Here is the acl

### Version information

If not matrix.org:

- **Version**: 1.47.1
- **python_version**: 3.9.2

- **Install method**: Official Debian package

- **Platform**: apt

Running on Debian 11 (Bullseye)

The report names no source file or test entry point; start by reproducing the room ACL and typing-notification behavior on Synapse 1.47.1, using the homeserver.log guidance if relevant. Trace how server ACLs are applied to typing notifications, then add coverage showing that a denied server's notifications are blocked and run the affected test suite.

Written by the indexing model from the issue text.