Clarify the error codes that can be returned with a 400 HTTP status code by the `POST /_matrix/identity/v2/validate/email/submitToken`
and `POST /_matrix/identity/v2/validate/msisdn/submitToken` endpoints, introducing the `M_TOKEN_INCORRECT`
error code, as per [MSC4183](https://github.com/matrix-org/matrix-spec-proposals/pull/4183).