Can't set pushrules for room with / or space in the roomid

This issue has been migrated from [#9938](https://github.com/matrix-org/synapse/issues/9938).

---

### Description

When trying to mute a room with a / or space in the room id (not sure what causes the issue here), synapse logs the following:

```
2021-05-06 12:02:11,700 - synapse.http.server - 88 - INFO - PUT-488390 - SynapseError: 400 - Unrecognized request
```

### Steps to reproduce

- create a room id with a / in it or so, like "!test/v6 :smile::maunium.net"
- Try to mute it in any client or via curl

I would expect the room to be muted, but the request fails, even for percent encoded parameters.

### Version information

- **Homeserver**:

If not matrix.org: neko.dev, maunium.net

- **Version**: 1.33.0

- **Install method**: package, docker

- **Platform**: Gentoo, Debian