Deactivating a user via the admin api + enabling the GDP erasure triggers a rejoin after the leaves

### Description

when using the [user deactivation admin api](https://element-hq.github.io/synapse/latest/admin_api/user_admin_api.html#deactivate-account) with the optional
```
{
"erase": true
}
```
the account in question gets properly deactivated AND THEN rejoins all rooms again at the end

### Steps to reproduce

- deactivate user with ` "erase": true`

### Homeserver

unredacted.org

### Synapse Version

1.149.1

### Installation Method

Other (please mention below)

### Database

PSQL

### Workers

Multiple workers

### Platform

mdad

### Configuration

_No response_

### Relevant log output

```shell
23:41
i-am-a-fake-user3 joined the room
23:43
i-am-a-fake-user3 removed their displayname
23:43
i-am-a-fake-user3 left the room
23:43
i-am-a-fake-user3 joined the room
```

### Anything else that would be useful to know?

_No response_

Start with the user deactivation admin API entry point documented at the linked user_admin_api.html section, and reproduce the flow with erase=true on a multi-worker homeserver. Trace the deactivation and erasure sequence against the reported log events; done means the account is deactivated and erased without rejoining its rooms.

Written by the indexing model from the issue text.