Cannot unban room member after triggering glitch

This issue has been migrated from [#15050](https://github.com/matrix-org/synapse/issues/15050).

---

### Description

I'm unable to unban a previous room member even though I have admin

### Steps to reproduce

- Ban some account from a room
- Give the account you banned admin while the account remains banned
- This account now cannot be unbanned, as unbanning involves changing the account room state from ban to leave and this implies kicking which is not allowed to be done to admins. You cannot invite either, as inviting a banned user does not work until the status is first set to leave

### Homeserver

does not matter

### Synapse Version

this also does not matter, at all.

### Installation Method

Debian packages from packages.matrix.org

### Database

PostgreSQL

### Workers

Single process

### Platform

Really the details do not matter here

### Configuration

Again, this isn't important.

### Relevant log output

```shell
None
```

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

Nope