Fix HiFi client not failing over to next instance on HTTP 500

Previously only 502/503/504 triggered instance rotation. A 500 from one
instance (e.g. triton.squid.wtf choking on a specific query) would stop
the search entirely instead of trying the next instance.

core/hifi_client.py

@@ -191,7 +191,7 @@ class HiFiClient:
                 self._rotate_instance(instance)
             except http_requests.exceptions.HTTPError as e:
                 status = e.response.status_code if e.response is not None else 0
-                if status in (502, 503, 504):
+                if status >= 500:
                     logger.warning(f"HiFi API server error ({status}): {instance}")
                     self._rotate_instance(instance)
                 else: