Accepts invalid room tags

This issue has been migrated from [#10519](https://github.com/matrix-org/synapse/issues/10519).

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### Description

### Steps to reproduce

- setRoomTag "test" with body: `{"order":"string"}`
- getRoomTags returns `{"tags":{"test":{"order":"string"}}}` which is non-conforming to the [spec](https://github.com/matrix-org/matrix-doc/blob/master/data/api/client-server/tags.yaml#L67)

Synapse should reject invalid setRoomTag operations like Dendrite and Conduit do. Synapse should never return invalid data from getRoomTags.

### Version information

- **Version**: 1.39.0