JSONDecodeError when trying to interact with user in a non-healthy server

We got a small federation running for Raiden Network, and because of some disk full issue, one of the servers crashed. Following it, the healthy ones started returning some unexpected responses for interactions with users on the healthy ones.
E.g. trying to invite an user in the unhealthy server to a room in the healthy one, the invite request returned:

<Response [429]>
{"errcode":"M_UNKNOWN","error":"Unknown Status"}

but from
https://github.com/matrix-org/matrix-python-sdk/blob/e366d52850f2bd948e9613022b735054616cfe0b/matrix_client/api.py#L731-L735
if the error isn't a json, json.JSONDecodeError will be raised.
Quick fix is to add json.JSONDecodeError to the handled errors in L734
Full stack traces and context can be found in raiden-network/raiden#2603

Start in matrix_client/api.py around lines 731-735, where non-JSON error responses are parsed and handled. Reproduce the 429 response containing the shown error payload, then verify that the interaction follows the existing handled-error path without raising JSONDecodeError.